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	$88.62	13.385%	$100.4818	$100.48	$100.50	$100.50
Purchase #2	$87.32	12.496%	$98.2315	$98.23	$98.25	$98.20
Purchase #3	$243.26	3.397%	$251.5235	$251.52	$251.50	$251.50
Purchase #4	$10.79	11.553%	$12.0366	$12.04	$12.05	$12.00
Purchase #5	$12.91	10.778%	$14.3014	$14.30	$14.30	$14.30
Purchase #6	$218.51	9.150%	$238.5037	$238.50	$238.50	$238.50
Purchase #7	$145.40	4.276%	$151.6173	$151.62	$151.60	$151.60
7 purchase totals =	$806.81		$866.6958	$866.69	$866.70	$866.60