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	$179.87	13.639%	$204.4025	$204.40	$204.40	$204.40
Purchase #2	$30.33	6.632%	$32.3415	$32.34	$32.35	$32.30
Purchase #3	$235.82	6.657%	$251.5185	$251.52	$251.50	$251.50
Purchase #4	$136.37	13.713%	$155.0704	$155.07	$155.05	$155.10
Purchase #5	$6.70	11.127%	$7.4455	$7.45	$7.45	$7.40
Purchase #6	$126.65	6.124%	$134.406	$134.41	$134.40	$134.40
Purchase #7	$100.73	10.481%	$111.2875	$111.29	$111.30	$111.30
7 purchase totals =	$816.47		$896.4719	$896.48	$896.45	$896.40