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	$50.73	10.730%	$56.1733	$56.17	$56.15	$56.20
Purchase #2	$37.85	12.213%	$42.4726	$42.47	$42.45	$42.50
Purchase #3	$108.94	4.684%	$114.0427	$114.04	$114.05	$114.00
Purchase #4	$210.42	11.164%	$233.9113	$233.91	$233.90	$233.90
Purchase #5	$76.89	3.523%	$79.5988	$79.60	$79.60	$79.60
Purchase #6	$204.63	5.771%	$216.4392	$216.44	$216.45	$216.40
Purchase #7	$55.43	10.206%	$61.0872	$61.09	$61.10	$61.10
7 purchase totals =	$744.89		$803.7251	$803.72	$803.70	$803.70