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 $60.71   3.734%   $62.9769   $62.98   $63.00   $63.00  
  Purchase #2 $63.41   8.677%   $68.9121   $68.91   $68.90   $68.90  
  Purchase #3 $44.54   8.412%   $48.2867   $48.29   $48.30   $48.30  
  Purchase #4 $242.36   4.503%   $253.2735   $253.27   $253.25   $253.30  
  Purchase #5 $145.38   8.642%   $157.9437   $157.94   $157.95   $157.90  
  Purchase #6 $66.62   6.333%   $70.839   $70.84   $70.85   $70.80  
  Purchase #7 $128.53   8.340%   $139.2494   $139.25   $139.25   $139.20  
  7 purchase totals = $751.55       $801.4813   $801.48   $801.50   $801.40