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 $92.76   4.827%   $97.2375   $97.24   $97.25   $97.20  
  Purchase #2 $178.85   11.608%   $199.6109   $199.61   $199.60   $199.60  
  Purchase #3 $115.35   8.417%   $125.059   $125.06   $125.05   $125.10  
  Purchase #4 $190.37   7.328%   $204.3203   $204.32   $204.30   $204.30  
  Purchase #5 $66.95   13.480%   $75.9749   $75.97   $75.95   $76.00  
  Purchase #6 $94.58   4.616%   $98.9458   $98.95   $98.95   $98.90  
  Purchase #7 $110.37   6.596%   $117.65   $117.65   $117.65   $117.70  
  7 purchase totals = $849.23       $918.7984   $918.80   $918.75   $918.80