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 $55.57   4.833%   $58.2557   $58.26   $58.25   $58.30  
  Purchase #2 $130.97   8.385%   $141.9518   $141.95   $141.95   $142.00  
  Purchase #3 $88.35   11.213%   $98.2567   $98.26   $98.25   $98.30  
  Purchase #4 $116.94   9.133%   $127.6201   $127.62   $127.60   $127.60  
  Purchase #5 $81.83   13.567%   $92.9319   $92.93   $92.95   $92.90  
  Purchase #6 $138.71   9.692%   $152.1538   $152.15   $152.15   $152.20  
  Purchase #7 $139.75   11.821%   $156.2698   $156.27   $156.25   $156.30  
  7 purchase totals = $752.12       $827.4398   $827.44   $827.40   $827.60