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 $194.37   6.114%   $206.2538   $206.25   $206.25   $206.30  
  Purchase #2 $160.50   8.240%   $173.7252   $173.73   $173.75   $173.70  
  Purchase #3 $130.32   5.179%   $137.0693   $137.07   $137.05   $137.10  
  Purchase #4 $156.99   10.774%   $173.9041   $173.90   $173.90   $173.90  
  Purchase #5 $43.94   3.692%   $45.5623   $45.56   $45.55   $45.60  
  Purchase #6 $5.81   10.657%   $6.4292   $6.43   $6.45   $6.40  
  Purchase #7 $208.44   5.196%   $219.2705   $219.27   $219.25   $219.30  
  7 purchase totals = $900.37       $962.2144   $962.21   $962.20   $962.30