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 $62.83   5.802%   $66.4754   $66.48   $66.50   $66.50  
  Purchase #2 $219.38   7.790%   $236.4697   $236.47   $236.45   $236.50  
  Purchase #3 $38.61   8.173%   $41.7656   $41.77   $41.75   $41.80  
  Purchase #4 $47.91   5.350%   $50.4732   $50.47   $50.45   $50.50  
  Purchase #5 $225.36   4.172%   $234.762   $234.76   $234.75   $234.80  
  Purchase #6 $93.67   3.689%   $97.1255   $97.13   $97.15   $97.10  
  Purchase #7 $180.48   3.211%   $186.2752   $186.28   $186.30   $186.30  
  7 purchase totals = $868.24       $913.3466   $913.36   $913.35   $913.50