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 $249.83   6.195%   $265.307   $265.31   $265.30   $265.30  
  Purchase #2 $92.33   3.871%   $95.9041   $95.90   $95.90   $95.90  
  Purchase #3 $248.78   4.113%   $259.0123   $259.01   $259.00   $259.00  
  Purchase #4 $162.88   10.164%   $179.4351   $179.44   $179.45   $179.40  
  Purchase #5 $191.60   5.844%   $202.7971   $202.80   $202.80   $202.80  
  Purchase #6 $6.76   12.847%   $7.6285   $7.63   $7.65   $7.60  
  Purchase #7 $225.76   13.129%   $255.4   $255.40   $255.40   $255.40  
  7 purchase totals = $1,177.94       $1,265.4841   $1,265.49   $1,265.50   $1,265.40