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	$176.33	12.762%	$198.8332	$198.83	$198.85	$198.80
Purchase #2	$120.56	8.436%	$130.7304	$130.73	$130.75	$130.70
Purchase #3	$57.27	4.471%	$59.8305	$59.83	$59.85	$59.80
Purchase #4	$89.42	13.520%	$101.5096	$101.51	$101.50	$101.50
Purchase #5	$138.89	7.348%	$149.0956	$149.10	$149.10	$149.10
Purchase #6	$223.35	3.183%	$230.4592	$230.46	$230.45	$230.50
Purchase #7	$242.41	4.271%	$252.7633	$252.76	$252.75	$252.80
7 purchase totals =	$1,048.23		$1,123.2218	$1,123.22	$1,123.25	$1,123.20