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 $152.88   6.216%   $162.383   $162.38   $162.40   $162.40  
  Purchase #2 $50.52   10.680%   $55.9155   $55.92   $55.90   $55.90  
  Purchase #3 $22.88   8.111%   $24.7358   $24.74   $24.75   $24.70  
  Purchase #4 $71.79   8.192%   $77.671   $77.67   $77.65   $77.70  
  Purchase #5 $100.27   13.184%   $113.4896   $113.49   $113.50   $113.50  
  Purchase #6 $69.36   8.681%   $75.3811   $75.38   $75.40   $75.40  
  Purchase #7 $229.74   10.323%   $253.4561   $253.46   $253.45   $253.50  
  7 purchase totals = $697.44       $763.0321   $763.04   $763.05   $763.10