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	$96.47	4.569%	$100.8777	$100.88	$100.90	$100.90
Purchase #2	$142.47	12.778%	$160.6748	$160.67	$160.65	$160.70
Purchase #3	$164.29	8.830%	$178.7968	$178.80	$178.80	$178.80
Purchase #4	$147.40	7.733%	$158.7984	$158.80	$158.80	$158.80
Purchase #5	$46.74	4.401%	$48.797	$48.80	$48.80	$48.80
Purchase #6	$61.73	8.537%	$66.9999	$67.00	$67.00	$67.00
Purchase #7	$119.61	6.204%	$127.0306	$127.03	$127.05	$127.00
7 purchase totals =	$778.71		$841.9752	$841.98	$842.00	$842.00