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 $56.95   12.114%   $63.8489   $63.85   $63.85   $63.80  
  Purchase #2 $213.41   10.401%   $235.6068   $235.61   $235.60   $235.60  
  Purchase #3 $156.82   6.766%   $167.4304   $167.43   $167.45   $167.40  
  Purchase #4 $51.85   6.316%   $55.1248   $55.12   $55.10   $55.10  
  Purchase #5 $110.80   6.682%   $118.2037   $118.20   $118.20   $118.20  
  Purchase #6 $80.46   8.743%   $87.4946   $87.49   $87.50   $87.50  
  Purchase #7 $157.76   10.726%   $174.6813   $174.68   $174.70   $174.70  
  7 purchase totals = $828.05       $902.3905   $902.38   $902.40   $902.30