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	$93.62	3.370%	$96.775	$96.78	$96.80	$96.80
Purchase #2	$97.96	13.745%	$111.4246	$111.42	$111.40	$111.40
Purchase #3	$249.49	11.813%	$278.9623	$278.96	$278.95	$279.00
Purchase #4	$57.40	3.376%	$59.3378	$59.34	$59.35	$59.30
Purchase #5	$149.56	7.759%	$161.1644	$161.16	$161.15	$161.20
Purchase #6	$142.26	4.366%	$148.4711	$148.47	$148.45	$148.50
Purchase #7	$77.27	13.190%	$87.4619	$87.46	$87.45	$87.50
7 purchase totals =	$867.56		$943.5971	$943.59	$943.55	$943.70