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 $64.93   4.758%   $68.0194   $68.02   $68.00   $68.00  
  Purchase #2 $132.50   11.857%   $148.2105   $148.21   $148.20   $148.20  
  Purchase #3 $217.71   9.202%   $237.7437   $237.74   $237.75   $237.70  
  Purchase #4 $175.54   6.588%   $187.1046   $187.10   $187.10   $187.10  
  Purchase #5 $187.28   6.233%   $198.9532   $198.95   $198.95   $199.00  
  Purchase #6 $21.85   6.197%   $23.204   $23.20   $23.20   $23.20  
  Purchase #7 $114.56   13.620%   $130.1631   $130.16   $130.15   $130.20  
  7 purchase totals = $914.37       $993.3985   $993.38   $993.35   $993.40