Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $162.79   13.433%   $184.6576   $184.66   $184.65   $184.70  
  Purchase #2 $49.92   13.103%   $56.461   $56.46   $56.45   $56.50  
  Purchase #3 $139.41   11.304%   $155.1689   $155.17   $155.15   $155.20  
  Purchase #4 $43.63   11.739%   $48.7517   $48.75   $48.75   $48.80  
  Purchase #5 $188.72   4.225%   $196.6934   $196.69   $196.70   $196.70  
  Purchase #6 $125.46   6.345%   $133.4204   $133.42   $133.40   $133.40  
  Purchase #7 $98.33   8.619%   $106.8051   $106.81   $106.80   $106.80  
  7 purchase totals = $808.26       $881.9581   $881.96   $881.90   $882.10