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 $86.34   12.808%   $97.3984   $97.40   $97.40   $97.40  
  Purchase #2 $112.27   9.633%   $123.085   $123.09   $123.10   $123.10  
  Purchase #3 $240.80   8.344%   $260.8924   $260.89   $260.90   $260.90  
  Purchase #4 $129.96   10.554%   $143.676   $143.68   $143.70   $143.70  
  Purchase #5 $62.87   10.147%   $69.2494   $69.25   $69.25   $69.20  
  Purchase #6 $53.29   5.314%   $56.1218   $56.12   $56.10   $56.10  
  Purchase #7 $62.57   3.839%   $64.9721   $64.97   $64.95   $65.00  
  7 purchase totals = $748.10       $815.3951   $815.40   $815.40   $815.40