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 $232.59   12.536%   $261.7475   $261.75   $261.75   $261.70  
  Purchase #2 $56.87   13.467%   $64.5287   $64.53   $64.55   $64.50  
  Purchase #3 $71.86   7.839%   $77.4931   $77.49   $77.50   $77.50  
  Purchase #4 $50.78   8.775%   $55.2359   $55.24   $55.25   $55.20  
  Purchase #5 $135.79   5.621%   $143.4228   $143.42   $143.40   $143.40  
  Purchase #6 $199.34   7.344%   $213.9795   $213.98   $214.00   $214.00  
  Purchase #7 $129.56   3.370%   $133.9262   $133.93   $133.95   $133.90  
  7 purchase totals = $876.79       $950.3337   $950.34   $950.40   $950.20