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 $242.95   11.552%   $271.0156   $271.02   $271.00   $271.00  
  Purchase #2 $119.36   11.507%   $133.0948   $133.09   $133.10   $133.10  
  Purchase #3 $154.54   11.863%   $172.8731   $172.87   $172.85   $172.90  
  Purchase #4 $25.77   11.572%   $28.7521   $28.75   $28.75   $28.80  
  Purchase #5 $197.57   4.693%   $206.842   $206.84   $206.85   $206.80  
  Purchase #6 $96.75   8.464%   $104.9389   $104.94   $104.95   $104.90  
  Purchase #7 $132.59   13.706%   $150.7628   $150.76   $150.75   $150.80  
  7 purchase totals = $969.53       $1,068.2793   $1,068.27   $1,068.25   $1,068.30