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 $83.94   12.282%   $94.2495   $94.25   $94.25   $94.20  
  Purchase #2 $214.92   12.363%   $241.4906   $241.49   $241.50   $241.50  
  Purchase #3 $7.89   9.747%   $8.659   $8.66   $8.65   $8.70  
  Purchase #4 $94.70   5.216%   $99.6396   $99.64   $99.65   $99.60  
  Purchase #5 $105.95   8.575%   $115.0352   $115.04   $115.05   $115.00  
  Purchase #6 $50.42   4.677%   $52.7781   $52.78   $52.80   $52.80  
  Purchase #7 $234.78   11.198%   $261.0707   $261.07   $261.05   $261.10  
  7 purchase totals = $792.60       $872.9227   $872.93   $872.95   $872.90