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 $239.66   7.593%   $257.8574   $257.86   $257.85   $257.90  
  Purchase #2 $149.82   12.105%   $167.9557   $167.96   $167.95   $168.00  
  Purchase #3 $58.40   13.106%   $66.0539   $66.05   $66.05   $66.10  
  Purchase #4 $89.83   6.558%   $95.7211   $95.72   $95.70   $95.70  
  Purchase #5 $116.76   7.422%   $125.4259   $125.43   $125.45   $125.40  
  Purchase #6 $165.60   5.577%   $174.8355   $174.84   $174.85   $174.80  
  Purchase #7 $52.32   5.281%   $55.083   $55.08   $55.10   $55.10  
  7 purchase totals = $872.39       $942.9325   $942.94   $942.95   $943.00