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 $248.86   13.615%   $282.7423   $282.74   $282.75   $282.70  
  Purchase #2 $60.73   10.660%   $67.2038   $67.20   $67.20   $67.20  
  Purchase #3 $232.89   3.377%   $240.7547   $240.75   $240.75   $240.80  
  Purchase #4 $132.93   6.275%   $141.2714   $141.27   $141.25   $141.30  
  Purchase #5 $80.76   9.590%   $88.5049   $88.50   $88.50   $88.50  
  Purchase #6 $191.55   13.773%   $217.9322   $217.93   $217.95   $217.90  
  Purchase #7 $168.84   11.855%   $188.856   $188.86   $188.85   $188.90  
  7 purchase totals = $1,116.56       $1,227.2653   $1,227.25   $1,227.25   $1,227.30