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 $244.67   5.526%   $258.1905   $258.19   $258.20   $258.20  
  Purchase #2 $232.46   8.822%   $252.9676   $252.97   $252.95   $253.00  
  Purchase #3 $250.43   9.785%   $274.9346   $274.93   $274.95   $274.90  
  Purchase #4 $84.92   9.376%   $92.8821   $92.88   $92.90   $92.90  
  Purchase #5 $158.66   7.613%   $170.7388   $170.74   $170.75   $170.70  
  Purchase #6 $125.73   5.533%   $132.6866   $132.69   $132.70   $132.70  
  Purchase #7 $185.82   7.290%   $199.3663   $199.37   $199.35   $199.40  
  7 purchase totals = $1,282.69       $1,381.7665   $1,381.77   $1,381.80   $1,381.80