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 $158.71   6.594%   $169.1753   $169.18   $169.20   $169.20  
  Purchase #2 $135.68   12.386%   $152.4853   $152.49   $152.50   $152.50  
  Purchase #3 $76.71   9.192%   $83.7612   $83.76   $83.75   $83.80  
  Purchase #4 $58.36   11.677%   $65.1747   $65.17   $65.15   $65.20  
  Purchase #5 $204.68   6.453%   $217.888   $217.89   $217.90   $217.90  
  Purchase #6 $201.87   4.626%   $211.2085   $211.21   $211.20   $211.20  
  Purchase #7 $69.91   7.653%   $75.2602   $75.26   $75.25   $75.30  
  7 purchase totals = $905.92       $974.9532   $974.96   $974.95   $975.10