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	$118.91	4.340%	$124.0707	$124.07	$124.05	$124.10
Purchase #2	$246.79	3.442%	$255.2845	$255.28	$255.30	$255.30
Purchase #3	$129.86	8.750%	$141.2228	$141.22	$141.20	$141.20
Purchase #4	$39.96	13.836%	$45.4889	$45.49	$45.50	$45.50
Purchase #5	$127.96	5.857%	$135.4546	$135.45	$135.45	$135.50
Purchase #6	$16.72	10.412%	$18.4609	$18.46	$18.45	$18.50
Purchase #7	$105.49	5.448%	$111.2371	$111.24	$111.25	$111.20
7 purchase totals =	$785.69		$831.2195	$831.21	$831.20	$831.30