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	$17.34	7.301%	$18.606	$18.61	$18.60	$18.60
Purchase #2	$116.29	10.852%	$128.9098	$128.91	$128.90	$128.90
Purchase #3	$40.88	11.619%	$45.6298	$45.63	$45.65	$45.60
Purchase #4	$151.55	13.466%	$171.9577	$171.96	$171.95	$172.00
Purchase #5	$246.51	10.194%	$271.6392	$271.64	$271.65	$271.60
Purchase #6	$66.66	4.422%	$69.6077	$69.61	$69.60	$69.60
Purchase #7	$134.56	4.207%	$140.2209	$140.22	$140.20	$140.20
7 purchase totals =	$773.79		$846.5711	$846.58	$846.55	$846.50