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 $24.73   3.474%   $25.5891   $25.59   $25.60   $25.60  
  Purchase #2 $132.53   10.739%   $146.7624   $146.76   $146.75   $146.80  
  Purchase #3 $122.40   8.421%   $132.7073   $132.71   $132.70   $132.70  
  Purchase #4 $92.34   6.420%   $98.2682   $98.27   $98.25   $98.30  
  Purchase #5 $107.55   4.521%   $112.4123   $112.41   $112.40   $112.40  
  Purchase #6 $225.37   12.536%   $253.6224   $253.62   $253.60   $253.60  
  Purchase #7 $62.60   9.360%   $68.4594   $68.46   $68.45   $68.50  
  7 purchase totals = $767.52       $837.8211   $837.82   $837.75   $837.90