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	$49.98	10.140%	$55.048	$55.05	$55.05	$55.00
Purchase #2	$198.78	4.470%	$207.6655	$207.67	$207.65	$207.70
Purchase #3	$72.47	8.611%	$78.7104	$78.71	$78.70	$78.70
Purchase #4	$183.58	9.624%	$201.2477	$201.25	$201.25	$201.20
Purchase #5	$94.35	6.219%	$100.2176	$100.22	$100.20	$100.20
Purchase #6	$57.60	6.685%	$61.4506	$61.45	$61.45	$61.50
Purchase #7	$106.37	5.215%	$111.9172	$111.92	$111.90	$111.90
7 purchase totals =	$763.13		$816.2570	$816.27	$816.20	$816.20