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 $217.27   8.105%   $234.8797   $234.88   $234.90   $234.90  
  Purchase #2 $153.29   10.861%   $169.9388   $169.94   $169.95   $169.90  
  Purchase #3 $146.45   11.624%   $163.4733   $163.47   $163.45   $163.50  
  Purchase #4 $66.31   7.344%   $71.1798   $71.18   $71.20   $71.20  
  Purchase #5 $229.41   6.140%   $243.4958   $243.50   $243.50   $243.50  
  Purchase #6 $127.53   9.161%   $139.213   $139.21   $139.20   $139.20  
  Purchase #7 $173.97   6.395%   $185.0954   $185.10   $185.10   $185.10  
  7 purchase totals = $1,114.23       $1,207.2758   $1,207.28   $1,207.30   $1,207.30