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 $62.48   4.426%   $65.2454   $65.25   $65.25   $65.20  
  Purchase #2 $230.90   12.652%   $260.1135   $260.11   $260.10   $260.10  
  Purchase #3 $189.73   10.475%   $209.6042   $209.60   $209.60   $209.60  
  Purchase #4 $169.81   4.419%   $177.3139   $177.31   $177.30   $177.30  
  Purchase #5 $28.27   4.418%   $29.519   $29.52   $29.50   $29.50  
  Purchase #6 $16.46   11.259%   $18.3132   $18.31   $18.30   $18.30  
  Purchase #7 $133.38   6.363%   $141.867   $141.87   $141.85   $141.90  
  7 purchase totals = $831.03       $901.9762   $901.97   $901.90   $901.90