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 $84.36   9.144%   $92.0739   $92.07   $92.05   $92.10  
  Purchase #2 $240.72   8.112%   $260.2472   $260.25   $260.25   $260.20  
  Purchase #3 $106.73   5.329%   $112.4176   $112.42   $112.40   $112.40  
  Purchase #4 $126.29   4.580%   $132.0741   $132.07   $132.05   $132.10  
  Purchase #5 $22.38   13.412%   $25.3816   $25.38   $25.40   $25.40  
  Purchase #6 $93.57   8.429%   $101.457   $101.46   $101.45   $101.50  
  Purchase #7 $223.32   4.366%   $233.0702   $233.07   $233.05   $233.10  
  7 purchase totals = $897.37       $956.7216   $956.72   $956.65   $956.80