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 $214.61   12.591%   $241.6315   $241.63   $241.65   $241.60  
  Purchase #2 $113.81   8.255%   $123.205   $123.21   $123.20   $123.20  
  Purchase #3 $31.42   6.153%   $33.3533   $33.35   $33.35   $33.40  
  Purchase #4 $74.79   13.236%   $84.6892   $84.69   $84.70   $84.70  
  Purchase #5 $226.37   10.303%   $249.6929   $249.69   $249.70   $249.70  
  Purchase #6 $55.71   8.215%   $60.2866   $60.29   $60.30   $60.30  
  Purchase #7 $106.46   12.487%   $119.7537   $119.75   $119.75   $119.80  
  7 purchase totals = $823.17       $912.6122   $912.61   $912.65   $912.70