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	$206.51	12.574%	$232.4766	$232.48	$232.50	$232.50
Purchase #2	$77.40	9.842%	$85.0177	$85.02	$85.00	$85.00
Purchase #3	$113.91	11.757%	$127.3024	$127.30	$127.30	$127.30
Purchase #4	$177.77	4.159%	$185.1635	$185.16	$185.15	$185.20
Purchase #5	$154.62	5.169%	$162.6123	$162.61	$162.60	$162.60
Purchase #6	$81.60	9.585%	$89.4214	$89.42	$89.40	$89.40
Purchase #7	$17.77	7.594%	$19.1195	$19.12	$19.10	$19.10
7 purchase totals =	$829.58		$901.1134	$901.11	$901.05	$901.10