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 $114.68   7.565%   $123.3555   $123.36   $123.35   $123.40  
  Purchase #2 $88.86   6.645%   $94.7647   $94.76   $94.75   $94.80  
  Purchase #3 $235.61   4.131%   $245.343   $245.34   $245.35   $245.30  
  Purchase #4 $176.94   10.533%   $195.5771   $195.58   $195.60   $195.60  
  Purchase #5 $14.72   3.385%   $15.2183   $15.22   $15.20   $15.20  
  Purchase #6 $65.57   6.461%   $69.8065   $69.81   $69.80   $69.80  
  Purchase #7 $47.65   8.746%   $51.8175   $51.82   $51.80   $51.80  
  7 purchase totals = $744.03       $795.8826   $795.89   $795.85   $795.90