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	$150.92	13.211%	$170.858	$170.86	$170.85	$170.90
Purchase #2	$89.64	12.561%	$100.8997	$100.90	$100.90	$100.90
Purchase #3	$221.85	11.467%	$247.2895	$247.29	$247.30	$247.30
Purchase #4	$201.42	12.288%	$226.1705	$226.17	$226.15	$226.20
Purchase #5	$77.25	10.388%	$85.2747	$85.27	$85.25	$85.30
Purchase #6	$109.80	12.231%	$123.2296	$123.23	$123.25	$123.20
Purchase #7	$184.27	11.485%	$205.4334	$205.43	$205.45	$205.40
7 purchase totals =	$1,035.15		$1,159.1554	$1,159.15	$1,159.15	$1,159.20