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 $23.53   8.267%   $25.4752   $25.48   $25.50   $25.50  
  Purchase #2 $139.73   13.480%   $158.5656   $158.57   $158.55   $158.60  
  Purchase #3 $213.81   4.853%   $224.1862   $224.19   $224.20   $224.20  
  Purchase #4 $31.27   11.490%   $34.8629   $34.86   $34.85   $34.90  
  Purchase #5 $224.44   10.438%   $247.867   $247.87   $247.85   $247.90  
  Purchase #6 $133.93   4.603%   $140.0948   $140.09   $140.10   $140.10  
  Purchase #7 $87.57   5.398%   $92.297   $92.30   $92.30   $92.30  
  7 purchase totals = $854.28       $923.3487   $923.36   $923.35   $923.50