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 $204.84   9.397%   $224.0888   $224.09   $224.10   $224.10  
  Purchase #2 $244.34   5.692%   $258.2478   $258.25   $258.25   $258.20  
  Purchase #3 $111.32   5.361%   $117.2879   $117.29   $117.30   $117.30  
  Purchase #4 $32.57   5.867%   $34.4809   $34.48   $34.50   $34.50  
  Purchase #5 $55.81   9.588%   $61.1611   $61.16   $61.15   $61.20  
  Purchase #6 $11.88   7.458%   $12.766   $12.77   $12.75   $12.80  
  Purchase #7 $236.38   8.202%   $255.7679   $255.77   $255.75   $255.80  
  7 purchase totals = $897.14       $963.8004   $963.81   $963.80   $963.90