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 $239.44   8.568%   $259.9552   $259.96   $259.95   $260.00  
  Purchase #2 $111.90   5.371%   $117.9101   $117.91   $117.90   $117.90  
  Purchase #3 $32.73   7.544%   $35.1992   $35.20   $35.20   $35.20  
  Purchase #4 $229.94   13.359%   $260.6577   $260.66   $260.65   $260.70  
  Purchase #5 $104.35   9.319%   $114.0744   $114.07   $114.05   $114.10  
  Purchase #6 $49.67   9.732%   $54.5039   $54.50   $54.50   $54.50  
  Purchase #7 $110.63   13.281%   $125.3228   $125.32   $125.30   $125.30  
  7 purchase totals = $878.66       $967.6233   $967.62   $967.55   $967.70