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 $110.40   8.246%   $119.5036   $119.50   $119.50   $119.50  
  Purchase #2 $64.82   12.508%   $72.9277   $72.93   $72.95   $72.90  
  Purchase #3 $164.30   3.108%   $169.4064   $169.41   $169.40   $169.40  
  Purchase #4 $215.67   12.654%   $242.9609   $242.96   $242.95   $243.00  
  Purchase #5 $140.74   11.733%   $157.253   $157.25   $157.25   $157.30  
  Purchase #6 $44.50   4.591%   $46.543   $46.54   $46.55   $46.50  
  Purchase #7 $137.80   4.330%   $143.7667   $143.77   $143.75   $143.80  
  7 purchase totals = $878.23       $952.3613   $952.36   $952.35   $952.40