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 $208.87   8.352%   $226.3148   $226.31   $226.30   $226.30  
  Purchase #2 $111.63   8.824%   $121.4802   $121.48   $121.50   $121.50  
  Purchase #3 $57.99   5.395%   $61.1186   $61.12   $61.10   $61.10  
  Purchase #4 $69.46   8.580%   $75.4197   $75.42   $75.40   $75.40  
  Purchase #5 $26.79   13.289%   $30.3501   $30.35   $30.35   $30.40  
  Purchase #6 $182.59   11.803%   $204.1411   $204.14   $204.15   $204.10  
  Purchase #7 $12.95   4.772%   $13.568   $13.57   $13.55   $13.60  
  7 purchase totals = $670.28       $732.3925   $732.39   $732.35   $732.40