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	$53.25	6.172%	$56.5366	$56.54	$56.55	$56.50
Purchase #2	$120.87	7.611%	$130.0694	$130.07	$130.05	$130.10
Purchase #3	$64.75	12.297%	$72.7123	$72.71	$72.70	$72.70
Purchase #4	$145.26	7.262%	$155.8088	$155.81	$155.80	$155.80
Purchase #5	$188.78	4.146%	$196.6068	$196.61	$196.60	$196.60
Purchase #6	$56.26	4.704%	$58.9065	$58.91	$58.90	$58.90
Purchase #7	$10.89	13.723%	$12.3844	$12.38	$12.40	$12.40
7 purchase totals =	$640.06		$683.0248	$683.03	$683.00	$683.00