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 $114.29   9.259%   $124.8721   $124.87   $124.85   $124.90  
  Purchase #2 $48.78   3.750%   $50.6093   $50.61   $50.60   $50.60  
  Purchase #3 $60.61   8.242%   $65.6055   $65.61   $65.60   $65.60  
  Purchase #4 $184.97   4.547%   $193.3806   $193.38   $193.40   $193.40  
  Purchase #5 $160.86   6.863%   $171.8998   $171.90   $171.90   $171.90  
  Purchase #6 $119.99   11.636%   $133.952   $133.95   $133.95   $134.00  
  Purchase #7 $60.57   7.478%   $65.0994   $65.10   $65.10   $65.10  
  7 purchase totals = $750.07       $805.4187   $805.42   $805.40   $805.50