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 $168.92   8.427%   $183.1549   $183.15   $183.15   $183.20  
  Purchase #2 $34.63   13.601%   $39.34   $39.34   $39.35   $39.30  
  Purchase #3 $125.97   8.143%   $136.2277   $136.23   $136.25   $136.20  
  Purchase #4 $49.34   4.152%   $51.3886   $51.39   $51.40   $51.40  
  Purchase #5 $34.64   3.310%   $35.7866   $35.79   $35.80   $35.80  
  Purchase #6 $76.40   11.128%   $84.9018   $84.90   $84.90   $84.90  
  Purchase #7 $228.27   3.807%   $236.9602   $236.96   $236.95   $237.00  
  7 purchase totals = $718.17       $767.7598   $767.76   $767.80   $767.80