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 $88.84   9.792%   $97.5392   $97.54   $97.55   $97.50  
  Purchase #2 $32.62   12.583%   $36.7246   $36.72   $36.70   $36.70  
  Purchase #3 $104.26   8.373%   $112.9897   $112.99   $113.00   $113.00  
  Purchase #4 $85.93   8.169%   $92.9496   $92.95   $92.95   $92.90  
  Purchase #5 $48.93   4.421%   $51.0932   $51.09   $51.10   $51.10  
  Purchase #6 $48.70   12.748%   $54.9083   $54.91   $54.90   $54.90  
  Purchase #7 $204.56   7.587%   $220.08   $220.08   $220.10   $220.10  
  7 purchase totals = $613.84       $666.2846   $666.28   $666.30   $666.20