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 $51.74   3.815%   $53.7139   $53.71   $53.70   $53.70  
  Purchase #2 $89.92   3.593%   $93.1508   $93.15   $93.15   $93.20  
  Purchase #3 $111.92   3.104%   $115.394   $115.39   $115.40   $115.40  
  Purchase #4 $31.68   4.683%   $33.1636   $33.16   $33.15   $33.20  
  Purchase #5 $51.57   13.452%   $58.5072   $58.51   $58.50   $58.50  
  Purchase #6 $86.65   10.124%   $95.4224   $95.42   $95.40   $95.40  
  Purchase #7 $244.80   7.201%   $262.428   $262.43   $262.45   $262.40  
  7 purchase totals = $668.28       $711.7799   $711.77   $711.75   $711.80