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 $200.51   13.173%   $226.9232   $226.92   $226.90   $226.90  
  Purchase #2 $216.28   9.858%   $237.6009   $237.60   $237.60   $237.60  
  Purchase #3 $54.35   11.500%   $60.6003   $60.60   $60.60   $60.60  
  Purchase #4 $125.53   8.519%   $136.2239   $136.22   $136.20   $136.20  
  Purchase #5 $14.35   8.794%   $15.6119   $15.61   $15.60   $15.60  
  Purchase #6 $139.96   13.371%   $158.6741   $158.67   $158.65   $158.70  
  Purchase #7 $192.81   3.708%   $199.9594   $199.96   $199.95   $200.00  
  7 purchase totals = $943.79       $1,035.5937   $1,035.58   $1,035.50   $1,035.60