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	$100.72	4.719%	$105.473	$105.47	$105.45	$105.50
Purchase #2	$188.36	6.459%	$200.5262	$200.53	$200.55	$200.50
Purchase #3	$100.86	4.519%	$105.4179	$105.42	$105.40	$105.40
Purchase #4	$141.75	12.255%	$159.1215	$159.12	$159.10	$159.10
Purchase #5	$129.30	13.458%	$146.7012	$146.70	$146.70	$146.70
Purchase #6	$47.56	5.441%	$50.1477	$50.15	$50.15	$50.10
Purchase #7	$72.74	5.326%	$76.6141	$76.61	$76.60	$76.60
7 purchase totals =	$781.29		$844.0016	$844.00	$843.95	$843.90