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 $55.59   13.224%   $62.9412   $62.94   $62.95   $62.90  
  Purchase #2 $218.86   13.759%   $248.9729   $248.97   $248.95   $249.00  
  Purchase #3 $161.34   7.446%   $173.3534   $173.35   $173.35   $173.40  
  Purchase #4 $187.25   4.643%   $195.944   $195.94   $195.95   $195.90  
  Purchase #5 $85.26   10.532%   $94.2396   $94.24   $94.25   $94.20  
  Purchase #6 $137.43   7.161%   $147.2714   $147.27   $147.25   $147.30  
  Purchase #7 $90.74   12.286%   $101.8883   $101.89   $101.90   $101.90  
  7 purchase totals = $936.47       $1,024.6108   $1,024.60   $1,024.60   $1,024.60