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 $245.86   5.210%   $258.6693   $258.67   $258.65   $258.70  
  Purchase #2 $164.91   5.285%   $173.6255   $173.63   $173.65   $173.60  
  Purchase #3 $198.37   3.248%   $204.8131   $204.81   $204.80   $204.80  
  Purchase #4 $176.77   6.591%   $188.4209   $188.42   $188.40   $188.40  
  Purchase #5 $83.48   13.788%   $94.9902   $94.99   $95.00   $95.00  
  Purchase #6 $207.84   3.680%   $215.4885   $215.49   $215.50   $215.50  
  Purchase #7 $90.59   6.178%   $96.1867   $96.19   $96.20   $96.20  
  7 purchase totals = $1,167.82       $1,232.1942   $1,232.20   $1,232.20   $1,232.20