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 $54.81   11.725%   $61.2365   $61.24   $61.25   $61.20  
  Purchase #2 $111.82   10.237%   $123.267   $123.27   $123.25   $123.30  
  Purchase #3 $68.63   12.851%   $77.4496   $77.45   $77.45   $77.40  
  Purchase #4 $173.61   9.388%   $189.9085   $189.91   $189.90   $189.90  
  Purchase #5 $114.79   4.454%   $119.9027   $119.90   $119.90   $119.90  
  Purchase #6 $206.90   8.367%   $224.2113   $224.21   $224.20   $224.20  
  Purchase #7 $24.70   3.541%   $25.5746   $25.57   $25.55   $25.60  
  7 purchase totals = $755.26       $821.5502   $821.55   $821.50   $821.50