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 $173.94   11.733%   $194.3484   $194.35   $194.35   $194.30  
  Purchase #2 $85.97   8.864%   $93.5904   $93.59   $93.60   $93.60  
  Purchase #3 $142.56   10.281%   $157.2166   $157.22   $157.20   $157.20  
  Purchase #4 $36.87   9.319%   $40.3059   $40.31   $40.30   $40.30  
  Purchase #5 $224.52   11.566%   $250.488   $250.49   $250.50   $250.50  
  Purchase #6 $116.85   7.332%   $125.4174   $125.42   $125.40   $125.40  
  Purchase #7 $84.31   8.414%   $91.4038   $91.40   $91.40   $91.40  
  7 purchase totals = $865.02       $952.7705   $952.78   $952.75   $952.70