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 $61.81   10.532%   $68.3198   $68.32   $68.30   $68.30  
  Purchase #2 $126.78   11.709%   $141.6247   $141.62   $141.60   $141.60  
  Purchase #3 $175.65   9.548%   $192.4211   $192.42   $192.40   $192.40  
  Purchase #4 $9.40   10.851%   $10.42   $10.42   $10.40   $10.40  
  Purchase #5 $245.27   5.667%   $259.1695   $259.17   $259.15   $259.20  
  Purchase #6 $193.93   12.158%   $217.508   $217.51   $217.50   $217.50  
  Purchase #7 $100.48   3.470%   $103.9667   $103.97   $103.95   $104.00  
  7 purchase totals = $913.32       $993.4298   $993.43   $993.30   $993.40