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 $225.31   7.249%   $241.6427   $241.64   $241.65   $241.60  
  Purchase #2 $104.48   13.552%   $118.6391   $118.64   $118.65   $118.60  
  Purchase #3 $131.86   12.573%   $148.4388   $148.44   $148.45   $148.40  
  Purchase #4 $84.86   6.393%   $90.2851   $90.29   $90.30   $90.30  
  Purchase #5 $189.63   9.314%   $207.2921   $207.29   $207.30   $207.30  
  Purchase #6 $44.53   8.191%   $48.1775   $48.18   $48.20   $48.20  
  Purchase #7 $170.42   12.517%   $191.7515   $191.75   $191.75   $191.80  
  7 purchase totals = $951.09       $1,046.2268   $1,046.23   $1,046.30   $1,046.20