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 $91.58   3.827%   $95.0848   $95.08   $95.10   $95.10  
  Purchase #2 $123.99   7.241%   $132.9681   $132.97   $132.95   $133.00  
  Purchase #3 $157.41   8.139%   $170.2216   $170.22   $170.20   $170.20  
  Purchase #4 $248.54   5.252%   $261.5933   $261.59   $261.60   $261.60  
  Purchase #5 $172.64   12.749%   $194.6499   $194.65   $194.65   $194.60  
  Purchase #6 $22.98   7.149%   $24.6228   $24.62   $24.60   $24.60  
  Purchase #7 $89.30   12.411%   $100.383   $100.38   $100.40   $100.40  
  7 purchase totals = $906.44       $979.5235   $979.51   $979.50   $979.50