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 $193.81   6.761%   $206.9135   $206.91   $206.90   $206.90  
  Purchase #2 $68.53   6.827%   $73.2085   $73.21   $73.20   $73.20  
  Purchase #3 $12.29   9.492%   $13.4566   $13.46   $13.45   $13.50  
  Purchase #4 $85.63   11.232%   $95.248   $95.25   $95.25   $95.20  
  Purchase #5 $59.64   11.466%   $66.4783   $66.48   $66.50   $66.50  
  Purchase #6 $164.31   7.116%   $176.0023   $176.00   $176.00   $176.00  
  Purchase #7 $56.95   12.632%   $64.1439   $64.14   $64.15   $64.10  
  7 purchase totals = $641.16       $695.4511   $695.45   $695.45   $695.40