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 $232.64   12.160%   $260.929   $260.93   $260.95   $260.90  
  Purchase #2 $47.97   13.582%   $54.4853   $54.49   $54.50   $54.50  
  Purchase #3 $44.91   4.456%   $46.9112   $46.91   $46.90   $46.90  
  Purchase #4 $92.67   11.369%   $103.2057   $103.21   $103.20   $103.20  
  Purchase #5 $171.82   13.110%   $194.3456   $194.35   $194.35   $194.30  
  Purchase #6 $48.39   10.660%   $53.5484   $53.55   $53.55   $53.50  
  Purchase #7 $44.38   10.138%   $48.8792   $48.88   $48.90   $48.90  
  7 purchase totals = $682.78       $762.3044   $762.32   $762.35   $762.20