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 $94.89   3.856%   $98.549   $98.55   $98.55   $98.50  
  Purchase #2 $133.47   7.708%   $143.7579   $143.76   $143.75   $143.80  
  Purchase #3 $77.61   10.622%   $85.8537   $85.85   $85.85   $85.90  
  Purchase #4 $88.37   8.771%   $96.1209   $96.12   $96.10   $96.10  
  Purchase #5 $147.57   7.782%   $159.0539   $159.05   $159.05   $159.10  
  Purchase #6 $145.53   8.177%   $157.43   $157.43   $157.45   $157.40  
  Purchase #7 $84.78   13.395%   $96.1363   $96.14   $96.15   $96.10  
  7 purchase totals = $772.22       $836.9017   $836.90   $836.90   $836.90