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 $227.41   11.232%   $252.9527   $252.95   $252.95   $253.00  
  Purchase #2 $158.75   10.511%   $175.4362   $175.44   $175.45   $175.40  
  Purchase #3 $211.61   3.728%   $219.4988   $219.50   $219.50   $219.50  
  Purchase #4 $85.78   12.125%   $96.1808   $96.18   $96.20   $96.20  
  Purchase #5 $217.43   8.869%   $236.7139   $236.71   $236.70   $236.70  
  Purchase #6 $87.55   7.377%   $94.0086   $94.01   $94.00   $94.00  
  Purchase #7 $164.77   4.759%   $172.6114   $172.61   $172.60   $172.60  
  7 purchase totals = $1,153.30       $1,247.4024   $1,247.40   $1,247.40   $1,247.40