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	$144.83	9.833%	$159.0711	$159.07	$159.05	$159.10
Purchase #2	$140.34	5.331%	$147.8215	$147.82	$147.80	$147.80
Purchase #3	$50.34	3.624%	$52.1643	$52.16	$52.15	$52.20
Purchase #4	$178.40	3.844%	$185.2577	$185.26	$185.25	$185.30
Purchase #5	$163.93	5.114%	$172.3134	$172.31	$172.30	$172.30
Purchase #6	$90.91	9.439%	$99.491	$99.49	$99.50	$99.50
Purchase #7	$96.62	9.381%	$105.6839	$105.68	$105.70	$105.70
7 purchase totals =	$865.37		$921.8029	$921.79	$921.75	$921.90