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	$194.66	13.703%	$221.3343	$221.33	$221.35	$221.30
Purchase #2	$35.85	13.156%	$40.5664	$40.57	$40.55	$40.60
Purchase #3	$138.58	10.795%	$153.5397	$153.54	$153.55	$153.50
Purchase #4	$34.60	3.293%	$35.7394	$35.74	$35.75	$35.70
Purchase #5	$231.41	12.414%	$260.1372	$260.14	$260.15	$260.10
Purchase #6	$29.55	11.184%	$32.8549	$32.85	$32.85	$32.90
Purchase #7	$153.49	12.337%	$172.4261	$172.43	$172.45	$172.40
7 purchase totals =	$818.14		$916.5980	$916.60	$916.65	$916.50