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 $217.86   4.541%   $227.753   $227.75   $227.75   $227.80  
  Purchase #2 $140.38   11.455%   $156.4605   $156.46   $156.45   $156.50  
  Purchase #3 $52.89   11.449%   $58.9454   $58.95   $58.95   $58.90  
  Purchase #4 $197.36   4.857%   $206.9458   $206.95   $206.95   $206.90  
  Purchase #5 $64.57   7.331%   $69.3036   $69.30   $69.30   $69.30  
  Purchase #6 $210.60   6.791%   $224.9018   $224.90   $224.90   $224.90  
  Purchase #7 $23.49   4.575%   $24.5647   $24.56   $24.55   $24.60  
  7 purchase totals = $907.15       $968.8748   $968.87   $968.85   $968.90