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	$118.31	10.298%	$130.4936	$130.49	$130.50	$130.50
Purchase #2	$49.40	10.400%	$54.5376	$54.54	$54.55	$54.50
Purchase #3	$101.95	9.354%	$111.4864	$111.49	$111.50	$111.50
Purchase #4	$175.78	8.722%	$191.1115	$191.11	$191.10	$191.10
Purchase #5	$241.74	13.794%	$275.0856	$275.09	$275.10	$275.10
Purchase #6	$159.42	13.328%	$180.6675	$180.67	$180.65	$180.70
Purchase #7	$183.95	7.315%	$197.4059	$197.41	$197.40	$197.40
7 purchase totals =	$1,030.55		$1,140.7881	$1,140.80	$1,140.80	$1,140.80