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 $114.44   10.272%   $126.1953   $126.20   $126.20   $126.20  
  Purchase #2 $69.68   10.258%   $76.8278   $76.83   $76.85   $76.80  
  Purchase #3 $177.57   5.251%   $186.8942   $186.89   $186.90   $186.90  
  Purchase #4 $172.26   13.354%   $195.2636   $195.26   $195.25   $195.30  
  Purchase #5 $84.37   10.612%   $93.3233   $93.32   $93.30   $93.30  
  Purchase #6 $90.38   8.582%   $98.1364   $98.14   $98.15   $98.10  
  Purchase #7 $150.46   5.232%   $158.3321   $158.33   $158.35   $158.30  
  7 purchase totals = $859.16       $934.9727   $934.97   $935.00   $934.90