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 $62.44   6.675%   $66.6079   $66.61   $66.60   $66.60  
  Purchase #2 $73.29   4.862%   $76.8534   $76.85   $76.85   $76.90  
  Purchase #3 $238.96   12.271%   $268.2828   $268.28   $268.30   $268.30  
  Purchase #4 $205.73   6.262%   $218.6128   $218.61   $218.60   $218.60  
  Purchase #5 $174.82   4.840%   $183.2813   $183.28   $183.30   $183.30  
  Purchase #6 $224.76   10.641%   $248.6767   $248.68   $248.70   $248.70  
  Purchase #7 $9.77   11.651%   $10.9083   $10.91   $10.90   $10.90  
  7 purchase totals = $989.77       $1,073.2232   $1,073.22   $1,073.25   $1,073.30