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 $55.77   6.315%   $59.2919   $59.29   $59.30   $59.30  
  Purchase #2 $38.75   10.611%   $42.8618   $42.86   $42.85   $42.90  
  Purchase #3 $195.68   11.277%   $217.7468   $217.75   $217.75   $217.70  
  Purchase #4 $23.94   5.341%   $25.2186   $25.22   $25.20   $25.20  
  Purchase #5 $219.68   8.252%   $237.808   $237.81   $237.80   $237.80  
  Purchase #6 $66.28   3.478%   $68.5852   $68.59   $68.60   $68.60  
  Purchase #7 $215.63   7.496%   $231.7936   $231.79   $231.80   $231.80  
  7 purchase totals = $815.73       $883.3059   $883.31   $883.30   $883.30