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 $44.35   13.473%   $50.3253   $50.33   $50.35   $50.30  
  Purchase #2 $239.34   11.576%   $267.046   $267.05   $267.05   $267.00  
  Purchase #3 $95.73   12.551%   $107.7451   $107.75   $107.75   $107.70  
  Purchase #4 $116.73   4.604%   $122.1042   $122.10   $122.10   $122.10  
  Purchase #5 $84.53   4.455%   $88.2958   $88.30   $88.30   $88.30  
  Purchase #6 $243.82   12.637%   $274.6315   $274.63   $274.65   $274.60  
  Purchase #7 $59.47   8.137%   $64.3091   $64.31   $64.30   $64.30  
  7 purchase totals = $883.97       $974.4570   $974.47   $974.50   $974.30