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 $21.84   12.458%   $24.5608   $24.56   $24.55   $24.60  
  Purchase #2 $240.49   7.213%   $257.8365   $257.84   $257.85   $257.80  
  Purchase #3 $191.80   7.216%   $205.6403   $205.64   $205.65   $205.60  
  Purchase #4 $214.64   9.708%   $235.4773   $235.48   $235.50   $235.50  
  Purchase #5 $171.48   3.861%   $178.1008   $178.10   $178.10   $178.10  
  Purchase #6 $21.48   9.380%   $23.4948   $23.49   $23.50   $23.50  
  Purchase #7 $93.32   5.612%   $98.5571   $98.56   $98.55   $98.60  
  7 purchase totals = $955.05       $1,023.6676   $1,023.67   $1,023.70   $1,023.70