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 $61.28   8.609%   $66.5556   $66.56   $66.55   $66.60  
  Purchase #2 $70.26   7.342%   $75.4185   $75.42   $75.40   $75.40  
  Purchase #3 $67.66   5.749%   $71.5498   $71.55   $71.55   $71.50  
  Purchase #4 $239.48   13.593%   $272.0325   $272.03   $272.05   $272.00  
  Purchase #5 $11.62   5.555%   $12.2655   $12.27   $12.25   $12.30  
  Purchase #6 $117.77   6.391%   $125.2967   $125.30   $125.30   $125.30  
  Purchase #7 $181.96   7.399%   $195.4232   $195.42   $195.40   $195.40  
  7 purchase totals = $750.03       $818.5418   $818.55   $818.50   $818.50