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	$215.93	13.365%	$244.789	$244.79	$244.80	$244.80
Purchase #2	$104.77	6.228%	$111.2951	$111.30	$111.30	$111.30
Purchase #3	$138.99	5.377%	$146.4635	$146.46	$146.45	$146.50
Purchase #4	$104.30	5.457%	$109.9917	$109.99	$110.00	$110.00
Purchase #5	$147.41	10.490%	$162.8733	$162.87	$162.85	$162.90
Purchase #6	$53.37	7.722%	$57.4912	$57.49	$57.50	$57.50
Purchase #7	$157.83	3.138%	$162.7827	$162.78	$162.80	$162.80
7 purchase totals =	$922.60		$995.6865	$995.68	$995.70	$995.80