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 $61.38   3.790%   $63.7063   $63.71   $63.70   $63.70  
  Purchase #2 $54.97   8.110%   $59.4281   $59.43   $59.45   $59.40  
  Purchase #3 $146.86   4.662%   $153.7066   $153.71   $153.70   $153.70  
  Purchase #4 $12.82   8.329%   $13.8878   $13.89   $13.90   $13.90  
  Purchase #5 $155.49   12.185%   $174.4365   $174.44   $174.45   $174.40  
  Purchase #6 $25.69   5.874%   $27.199   $27.20   $27.20   $27.20  
  Purchase #7 $126.44   4.546%   $132.188   $132.19   $132.20   $132.20  
  7 purchase totals = $583.65       $624.5523   $624.57   $624.60   $624.50