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 $59.90   4.720%   $62.7273   $62.73   $62.75   $62.70  
  Purchase #2 $36.38   13.626%   $41.3371   $41.34   $41.35   $41.30  
  Purchase #3 $212.54   11.346%   $236.6548   $236.65   $236.65   $236.70  
  Purchase #4 $177.87   3.396%   $183.9105   $183.91   $183.90   $183.90  
  Purchase #5 $15.52   9.644%   $17.0167   $17.02   $17.00   $17.00  
  Purchase #6 $35.29   3.208%   $36.4221   $36.42   $36.40   $36.40  
  Purchase #7 $14.87   3.411%   $15.3772   $15.38   $15.40   $15.40  
  7 purchase totals = $552.37       $593.4457   $593.45   $593.45   $593.40