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 $74.27   3.102%   $76.5739   $76.57   $76.55   $76.60  
  Purchase #2 $65.50   4.644%   $68.5418   $68.54   $68.55   $68.50  
  Purchase #3 $128.43   4.391%   $134.0694   $134.07   $134.05   $134.10  
  Purchase #4 $187.66   4.295%   $195.72   $195.72   $195.70   $195.70  
  Purchase #5 $116.58   9.147%   $127.2436   $127.24   $127.25   $127.20  
  Purchase #6 $217.92   4.559%   $227.855   $227.86   $227.85   $227.90  
  Purchase #7 $27.70   5.263%   $29.1579   $29.16   $29.15   $29.20  
  7 purchase totals = $818.06       $859.1616   $859.16   $859.10   $859.20