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	$85.89	5.194%	$90.3511	$90.35	$90.35	$90.40
Purchase #2	$233.59	5.803%	$247.1452	$247.15	$247.15	$247.10
Purchase #3	$12.50	8.721%	$13.5901	$13.59	$13.60	$13.60
Purchase #4	$141.94	4.461%	$148.2719	$148.27	$148.25	$148.30
Purchase #5	$40.89	10.227%	$45.0718	$45.07	$45.05	$45.10
Purchase #6	$112.61	13.557%	$127.8765	$127.88	$127.90	$127.90
Purchase #7	$46.45	11.501%	$51.7922	$51.79	$51.80	$51.80
7 purchase totals =	$673.87		$724.0988	$724.10	$724.10	$724.20