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 $64.69   13.196%   $73.2265   $73.23   $73.25   $73.20  
  Purchase #2 $40.81   11.517%   $45.5101   $45.51   $45.50   $45.50  
  Purchase #3 $237.29   4.817%   $248.7203   $248.72   $248.70   $248.70  
  Purchase #4 $142.92   11.689%   $159.6259   $159.63   $159.65   $159.60  
  Purchase #5 $86.45   13.143%   $97.8121   $97.81   $97.80   $97.80  
  Purchase #6 $60.32   4.411%   $62.9807   $62.98   $63.00   $63.00  
  Purchase #7 $74.76   12.864%   $84.3771   $84.38   $84.40   $84.40  
  7 purchase totals = $707.24       $772.2527   $772.26   $772.30   $772.20