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 $208.27   10.292%   $229.7051   $229.71   $229.70   $229.70  
  Purchase #2 $76.90   13.368%   $87.18   $87.18   $87.20   $87.20  
  Purchase #3 $47.35   13.625%   $53.8014   $53.80   $53.80   $53.80  
  Purchase #4 $139.74   13.684%   $158.862   $158.86   $158.85   $158.90  
  Purchase #5 $87.97   5.520%   $92.8259   $92.83   $92.85   $92.80  
  Purchase #6 $81.86   3.131%   $84.423   $84.42   $84.40   $84.40  
  Purchase #7 $216.34   3.516%   $223.9465   $223.95   $223.95   $223.90  
  7 purchase totals = $858.43       $930.7439   $930.75   $930.75   $930.70