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 $187.62   11.268%   $208.761   $208.76   $208.75   $208.80  
  Purchase #2 $113.26   12.177%   $127.0517   $127.05   $127.05   $127.10  
  Purchase #3 $41.67   12.386%   $46.8312   $46.83   $46.85   $46.80  
  Purchase #4 $161.65   5.173%   $170.0122   $170.01   $170.00   $170.00  
  Purchase #5 $235.51   10.487%   $260.2079   $260.21   $260.20   $260.20  
  Purchase #6 $56.95   3.154%   $58.7462   $58.75   $58.75   $58.70  
  Purchase #7 $66.41   8.103%   $71.7912   $71.79   $71.80   $71.80  
  7 purchase totals = $863.07       $943.4014   $943.40   $943.40   $943.40