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	$90.58	11.274%	$100.792	$100.79	$100.80	$100.80
Purchase #2	$146.55	4.752%	$153.5141	$153.51	$153.50	$153.50
Purchase #3	$145.44	4.118%	$151.4292	$151.43	$151.45	$151.40
Purchase #4	$31.92	12.155%	$35.7999	$35.80	$35.80	$35.80
Purchase #5	$183.51	5.152%	$192.9644	$192.96	$192.95	$193.00
Purchase #6	$80.28	12.359%	$90.2018	$90.20	$90.20	$90.20
Purchase #7	$105.25	6.714%	$112.3165	$112.32	$112.30	$112.30
7 purchase totals =	$783.53		$837.0179	$837.01	$837.00	$837.00