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 $91.52   6.401%   $97.3782   $97.38   $97.40   $97.40  
  Purchase #2 $162.74   3.183%   $167.92   $167.92   $167.90   $167.90  
  Purchase #3 $237.61   7.265%   $254.8724   $254.87   $254.85   $254.90  
  Purchase #4 $59.38   12.767%   $66.961   $66.96   $66.95   $67.00  
  Purchase #5 $69.92   11.744%   $78.1314   $78.13   $78.15   $78.10  
  Purchase #6 $104.34   8.584%   $113.2965   $113.30   $113.30   $113.30  
  Purchase #7 $185.65   9.256%   $202.8338   $202.83   $202.85   $202.80  
  7 purchase totals = $911.16       $981.3933   $981.39   $981.40   $981.40