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 $242.49   4.854%   $254.2605   $254.26   $254.25   $254.30  
  Purchase #2 $229.86   3.377%   $237.6224   $237.62   $237.60   $237.60  
  Purchase #3 $200.37   9.409%   $219.2228   $219.22   $219.20   $219.20  
  Purchase #4 $75.45   5.283%   $79.436   $79.44   $79.45   $79.40  
  Purchase #5 $106.36   7.106%   $113.9179   $113.92   $113.90   $113.90  
  Purchase #6 $236.90   3.174%   $244.4192   $244.42   $244.40   $244.40  
  Purchase #7 $69.72   13.405%   $79.066   $79.07   $79.05   $79.10  
  7 purchase totals = $1,161.15       $1,227.9448   $1,227.95   $1,227.85   $1,227.90