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 $205.58   13.521%   $233.3765   $233.38   $233.40   $233.40  
  Purchase #2 $139.73   11.212%   $155.3965   $155.40   $155.40   $155.40  
  Purchase #3 $34.93   3.593%   $36.185   $36.19   $36.20   $36.20  
  Purchase #4 $68.92   5.768%   $72.8953   $72.90   $72.90   $72.90  
  Purchase #5 $71.34   4.808%   $74.77   $74.77   $74.75   $74.80  
  Purchase #6 $124.86   3.405%   $129.1115   $129.11   $129.10   $129.10  
  Purchase #7 $226.85   8.343%   $245.7761   $245.78   $245.80   $245.80  
  7 purchase totals = $872.21       $947.5109   $947.53   $947.55   $947.60