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 $218.98   10.785%   $242.597   $242.60   $242.60   $242.60  
  Purchase #2 $239.46   4.271%   $249.6873   $249.69   $249.70   $249.70  
  Purchase #3 $249.67   4.618%   $261.1998   $261.20   $261.20   $261.20  
  Purchase #4 $97.84   12.820%   $110.3831   $110.38   $110.40   $110.40  
  Purchase #5 $102.49   9.562%   $112.2901   $112.29   $112.30   $112.30  
  Purchase #6 $155.33   6.420%   $165.3022   $165.30   $165.30   $165.30  
  Purchase #7 $136.84   11.575%   $152.6792   $152.68   $152.70   $152.70  
  7 purchase totals = $1,200.61       $1,294.1387   $1,294.14   $1,294.20   $1,294.20