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	$120.51	9.104%	$131.4812	$131.48	$131.50	$131.50
Purchase #2	$158.83	3.832%	$164.9164	$164.92	$164.90	$164.90
Purchase #3	$19.37	5.603%	$20.4553	$20.46	$20.45	$20.50
Purchase #4	$90.89	10.220%	$100.179	$100.18	$100.20	$100.20
Purchase #5	$9.26	10.502%	$10.2325	$10.23	$10.25	$10.20
Purchase #6	$153.45	8.361%	$166.28	$166.28	$166.30	$166.30
Purchase #7	$229.72	10.105%	$252.9332	$252.93	$252.95	$252.90
7 purchase totals =	$782.03		$846.4776	$846.48	$846.55	$846.50