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 $204.53   9.282%   $223.5145   $223.51   $223.50   $223.50  
  Purchase #2 $118.47   11.251%   $131.7991   $131.80   $131.80   $131.80  
  Purchase #3 $247.80   7.425%   $266.1992   $266.20   $266.20   $266.20  
  Purchase #4 $105.83   4.296%   $110.3765   $110.38   $110.40   $110.40  
  Purchase #5 $226.81   12.744%   $255.7147   $255.71   $255.70   $255.70  
  Purchase #6 $248.69   7.423%   $267.1503   $267.15   $267.15   $267.20  
  Purchase #7 $195.67   9.446%   $214.153   $214.15   $214.15   $214.20  
  7 purchase totals = $1,347.80       $1,468.9073   $1,468.90   $1,468.90   $1,469.00