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 $46.42   4.677%   $48.5911   $48.59   $48.60   $48.60  
  Purchase #2 $15.57   5.139%   $16.3701   $16.37   $16.35   $16.40  
  Purchase #3 $34.72   5.773%   $36.7244   $36.72   $36.70   $36.70  
  Purchase #4 $240.52   5.477%   $253.6933   $253.69   $253.70   $253.70  
  Purchase #5 $14.29   9.712%   $15.6778   $15.68   $15.70   $15.70  
  Purchase #6 $180.69   3.703%   $187.381   $187.38   $187.40   $187.40  
  Purchase #7 $130.62   4.222%   $136.1348   $136.13   $136.15   $136.10  
  7 purchase totals = $662.83       $694.5725   $694.56   $694.60   $694.60