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 $64.87   8.189%   $70.1822   $70.18   $70.20   $70.20  
  Purchase #2 $114.77   9.226%   $125.3587   $125.36   $125.35   $125.40  
  Purchase #3 $139.53   11.405%   $155.4434   $155.44   $155.45   $155.40  
  Purchase #4 $65.92   3.139%   $67.9892   $67.99   $68.00   $68.00  
  Purchase #5 $30.87   6.222%   $32.7907   $32.79   $32.80   $32.80  
  Purchase #6 $224.58   5.411%   $236.732   $236.73   $236.75   $236.70  
  Purchase #7 $195.80   12.170%   $219.6289   $219.63   $219.65   $219.60  
  7 purchase totals = $836.34       $908.1251   $908.12   $908.20   $908.10