BigDecimal code critique
For such a simple calculation, the logic used for the bdtip and bdtotal variables wasnt straight forward. Instead of creating it with the value of one of the operands, then multiplying/adding it by the other operand, why not do something like the following:

txt_check = txtcheck.getText().toString();
tpercent = txttippct.getText().toString();

BigDecimal hundred = new BigDecimal("100");
BigDecimal pct = new BigDecimal(tpercent);

BigDecimal bdpercent = pct.divide(hundred, 2, BigDecimal.ROUND_UNNECESSARY); 
BigDecimal bdcheck = new BigDecimal(txt_check);

BigDecimal bdtip = bdcheck.mulitply(bdpercent);
BigDecimal bdtotal = bdcheck.add(bdtip);