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	$199.91	12.118%	$224.1351	$224.14	$224.15	$224.10
Purchase #2	$179.91	11.632%	$200.8371	$200.84	$200.85	$200.80
Purchase #3	$127.32	13.773%	$144.8558	$144.86	$144.85	$144.90
Purchase #4	$55.62	3.745%	$57.703	$57.70	$57.70	$57.70
Purchase #5	$151.89	3.284%	$156.8781	$156.88	$156.90	$156.90
Purchase #6	$9.51	8.179%	$10.2878	$10.29	$10.30	$10.30
Purchase #7	$32.88	5.294%	$34.6207	$34.62	$34.60	$34.60
7 purchase totals =	$757.04		$829.3176	$829.33	$829.35	$829.30