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 $236.59   6.826%   $252.7396   $252.74   $252.75   $252.70  
  Purchase #2 $120.31   5.157%   $126.5144   $126.51   $126.50   $126.50  
  Purchase #3 $231.59   4.245%   $241.421   $241.42   $241.40   $241.40  
  Purchase #4 $110.44   13.855%   $125.7415   $125.74   $125.75   $125.70  
  Purchase #5 $6.73   9.479%   $7.3679   $7.37   $7.35   $7.40  
  Purchase #6 $241.89   7.559%   $260.1745   $260.17   $260.15   $260.20  
  Purchase #7 $196.77   10.820%   $218.0605   $218.06   $218.05   $218.10  
  7 purchase totals = $1,144.32       $1,232.0194   $1,232.01   $1,231.95   $1,232.00