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 $246.44   6.276%   $261.9066   $261.91   $261.90   $261.90  
  Purchase #2 $231.49   9.471%   $253.4144   $253.41   $253.40   $253.40  
  Purchase #3 $180.78   5.540%   $190.7952   $190.80   $190.80   $190.80  
  Purchase #4 $197.74   9.600%   $216.723   $216.72   $216.70   $216.70  
  Purchase #5 $76.26   10.172%   $84.0172   $84.02   $84.00   $84.00  
  Purchase #6 $222.53   7.572%   $239.38   $239.38   $239.40   $239.40  
  Purchase #7 $6.92   9.773%   $7.5963   $7.60   $7.60   $7.60  
  7 purchase totals = $1,162.16       $1,253.8327   $1,253.84   $1,253.80   $1,253.80