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 $208.45   9.199%   $227.6253   $227.63   $227.65   $227.60  
  Purchase #2 $151.31   12.326%   $169.9605   $169.96   $169.95   $170.00  
  Purchase #3 $72.88   11.798%   $81.4784   $81.48   $81.50   $81.50  
  Purchase #4 $164.25   7.564%   $176.6739   $176.67   $176.65   $176.70  
  Purchase #5 $91.87   8.285%   $99.4814   $99.48   $99.50   $99.50  
  Purchase #6 $45.42   7.408%   $48.7847   $48.78   $48.80   $48.80  
  Purchase #7 $42.39   9.664%   $46.4866   $46.49   $46.50   $46.50  
  7 purchase totals = $776.57       $850.4908   $850.49   $850.55   $850.60