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 $146.71   7.387%   $157.5475   $157.55   $157.55   $157.50  
  Purchase #2 $195.48   12.202%   $219.3325   $219.33   $219.35   $219.30  
  Purchase #3 $226.91   9.211%   $247.8107   $247.81   $247.80   $247.80  
  Purchase #4 $247.63   4.411%   $258.553   $258.55   $258.55   $258.60  
  Purchase #5 $8.28   7.177%   $8.8743   $8.87   $8.85   $8.90  
  Purchase #6 $103.32   12.109%   $115.831   $115.83   $115.85   $115.80  
  Purchase #7 $13.91   10.278%   $15.3397   $15.34   $15.35   $15.30  
  7 purchase totals = $942.24       $1,023.2887   $1,023.28   $1,023.30   $1,023.20