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 $54.79   3.316%   $56.6068   $56.61   $56.60   $56.60  
  Purchase #2 $239.25   12.618%   $269.4386   $269.44   $269.45   $269.40  
  Purchase #3 $149.40   13.249%   $169.194   $169.19   $169.20   $169.20  
  Purchase #4 $86.51   13.195%   $97.925   $97.93   $97.95   $97.90  
  Purchase #5 $136.95   12.566%   $154.1591   $154.16   $154.15   $154.20  
  Purchase #6 $36.34   13.674%   $41.3091   $41.31   $41.30   $41.30  
  Purchase #7 $65.61   9.153%   $71.6153   $71.62   $71.60   $71.60  
  7 purchase totals = $768.85       $860.2479   $860.26   $860.25   $860.20