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	$203.59	11.410%	$226.8196	$226.82	$226.80	$226.80
Purchase #2	$49.44	9.130%	$53.9539	$53.95	$53.95	$54.00
Purchase #3	$102.66	6.224%	$109.0496	$109.05	$109.05	$109.00
Purchase #4	$40.76	3.556%	$42.2094	$42.21	$42.20	$42.20
Purchase #5	$154.44	12.223%	$173.3172	$173.32	$173.30	$173.30
Purchase #6	$20.68	4.427%	$21.5955	$21.60	$21.60	$21.60
Purchase #7	$49.82	13.342%	$56.467	$56.47	$56.45	$56.50
7 purchase totals =	$621.39		$683.4122	$683.42	$683.35	$683.40