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	$203.51	12.846%	$229.6529	$229.65	$229.65	$229.70
Purchase #2	$34.45	11.738%	$38.4937	$38.49	$38.50	$38.50
Purchase #3	$100.28	8.849%	$109.1538	$109.15	$109.15	$109.20
Purchase #4	$122.52	4.147%	$127.6009	$127.60	$127.60	$127.60
Purchase #5	$94.77	11.714%	$105.8714	$105.87	$105.85	$105.90
Purchase #6	$202.60	8.506%	$219.8332	$219.83	$219.85	$219.80
Purchase #7	$54.32	9.374%	$59.412	$59.41	$59.40	$59.40
7 purchase totals =	$812.45		$890.0179	$890.00	$890.00	$890.10