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	$198.35	12.142%	$222.4337	$222.43	$222.45	$222.40
Purchase #2	$94.75	7.461%	$101.8193	$101.82	$101.80	$101.80
Purchase #3	$31.95	6.552%	$34.0434	$34.04	$34.05	$34.00
Purchase #4	$117.88	8.479%	$127.875	$127.88	$127.90	$127.90
Purchase #5	$96.50	11.512%	$107.6091	$107.61	$107.60	$107.60
Purchase #6	$116.91	11.209%	$130.0144	$130.01	$130.00	$130.00
Purchase #7	$87.45	10.521%	$96.6506	$96.65	$96.65	$96.70
7 purchase totals =	$743.79		$820.4455	$820.44	$820.45	$820.40