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	$119.79	11.448%	$133.5036	$133.50	$133.50	$133.50
Purchase #2	$36.63	11.176%	$40.7238	$40.72	$40.70	$40.70
Purchase #3	$66.33	4.499%	$69.3142	$69.31	$69.30	$69.30
Purchase #4	$82.95	10.337%	$91.5245	$91.52	$91.50	$91.50
Purchase #5	$113.99	8.195%	$123.3315	$123.33	$123.35	$123.30
Purchase #6	$109.84	13.598%	$124.776	$124.78	$124.80	$124.80
Purchase #7	$88.61	13.344%	$100.4341	$100.43	$100.45	$100.40
7 purchase totals =	$618.14		$683.6077	$683.59	$683.60	$683.50