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	$63.38	11.679%	$70.7822	$70.78	$70.80	$70.80
Purchase #2	$227.61	11.667%	$254.1653	$254.17	$254.15	$254.20
Purchase #3	$23.72	8.858%	$25.8211	$25.82	$25.80	$25.80
Purchase #4	$141.76	7.858%	$152.8995	$152.90	$152.90	$152.90
Purchase #5	$89.71	12.715%	$101.1166	$101.12	$101.10	$101.10
Purchase #6	$12.72	7.730%	$13.7033	$13.70	$13.70	$13.70
Purchase #7	$229.71	13.196%	$260.0225	$260.02	$260.00	$260.00
7 purchase totals =	$788.61		$878.5105	$878.51	$878.45	$878.50