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	$141.29	12.630%	$159.1349	$159.13	$159.15	$159.10
Purchase #2	$211.51	13.431%	$239.9179	$239.92	$239.90	$239.90
Purchase #3	$134.60	3.619%	$139.4712	$139.47	$139.45	$139.50
Purchase #4	$213.70	11.581%	$238.4486	$238.45	$238.45	$238.40
Purchase #5	$42.35	10.284%	$46.7053	$46.71	$46.70	$46.70
Purchase #6	$216.69	7.769%	$233.5246	$233.52	$233.50	$233.50
Purchase #7	$250.50	8.327%	$271.3591	$271.36	$271.35	$271.40
7 purchase totals =	$1,210.64		$1,328.5616	$1,328.56	$1,328.50	$1,328.50