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 $19.90   12.512%   $22.3899   $22.39   $22.40   $22.40  
  Purchase #2 $120.46   10.807%   $133.4781   $133.48   $133.50   $133.50  
  Purchase #3 $142.46   10.473%   $157.3798   $157.38   $157.40   $157.40  
  Purchase #4 $61.38   6.592%   $65.4262   $65.43   $65.45   $65.40  
  Purchase #5 $54.35   7.582%   $58.4708   $58.47   $58.45   $58.50  
  Purchase #6 $184.57   9.630%   $202.3441   $202.34   $202.35   $202.30  
  Purchase #7 $140.41   4.639%   $146.9236   $146.92   $146.90   $146.90  
  7 purchase totals = $723.53       $786.4125   $786.41   $786.45   $786.40