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 $58.96   6.394%   $62.7299   $62.73   $62.75   $62.70  
  Purchase #2 $34.59   8.154%   $37.4105   $37.41   $37.40   $37.40  
  Purchase #3 $229.54   4.736%   $240.411   $240.41   $240.40   $240.40  
  Purchase #4 $220.95   7.472%   $237.4594   $237.46   $237.45   $237.50  
  Purchase #5 $192.73   10.639%   $213.2345   $213.23   $213.25   $213.20  
  Purchase #6 $234.88   12.718%   $264.752   $264.75   $264.75   $264.80  
  Purchase #7 $232.92   10.713%   $257.8727   $257.87   $257.85   $257.90  
  7 purchase totals = $1,204.57       $1,313.8700   $1,313.86   $1,313.85   $1,313.90