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	$180.57	13.258%	$204.51	$204.51	$204.50	$204.50
Purchase #2	$155.94	13.863%	$177.558	$177.56	$177.55	$177.60
Purchase #3	$34.38	9.469%	$37.6354	$37.64	$37.65	$37.60
Purchase #4	$168.48	7.147%	$180.5213	$180.52	$180.50	$180.50
Purchase #5	$186.86	3.549%	$193.4917	$193.49	$193.50	$193.50
Purchase #6	$37.37	12.420%	$42.0114	$42.01	$42.00	$42.00
Purchase #7	$234.59	8.833%	$255.3113	$255.31	$255.30	$255.30
7 purchase totals =	$998.19		$1,091.0391	$1,091.04	$1,091.00	$1,091.00