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 $22.60   7.249%   $24.2383   $24.24   $24.25   $24.20  
  Purchase #2 $61.95   12.184%   $69.498   $69.50   $69.50   $69.50  
  Purchase #3 $136.74   8.506%   $148.3711   $148.37   $148.35   $148.40  
  Purchase #4 $10.38   8.543%   $11.2668   $11.27   $11.25   $11.30  
  Purchase #5 $163.34   8.642%   $177.4558   $177.46   $177.45   $177.50  
  Purchase #6 $59.27   11.863%   $66.3012   $66.30   $66.30   $66.30  
  Purchase #7 $216.91   7.189%   $232.5037   $232.50   $232.50   $232.50  
  7 purchase totals = $671.19       $729.6349   $729.64   $729.60   $729.70