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 $223.50   13.621%   $253.9429   $253.94   $253.95   $253.90  
  Purchase #2 $58.33   3.814%   $60.5547   $60.55   $60.55   $60.60  
  Purchase #3 $126.30   5.471%   $133.2099   $133.21   $133.20   $133.20  
  Purchase #4 $188.95   8.154%   $204.357   $204.36   $204.35   $204.40  
  Purchase #5 $112.64   13.176%   $127.4814   $127.48   $127.50   $127.50  
  Purchase #6 $158.86   9.863%   $174.5284   $174.53   $174.55   $174.50  
  Purchase #7 $214.75   7.237%   $230.2915   $230.29   $230.30   $230.30  
  7 purchase totals = $1,083.33       $1,184.3658   $1,184.36   $1,184.40   $1,184.40