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	$17.31	7.857%	$18.67	$18.67	$18.65	$18.70
Purchase #2	$236.77	12.549%	$266.4823	$266.48	$266.50	$266.50
Purchase #3	$69.28	13.532%	$78.655	$78.66	$78.65	$78.70
Purchase #4	$121.57	9.433%	$133.0377	$133.04	$133.05	$133.00
Purchase #5	$155.77	11.227%	$173.2583	$173.26	$173.25	$173.30
Purchase #6	$222.67	7.263%	$238.8425	$238.84	$238.85	$238.80
Purchase #7	$97.41	10.790%	$107.9205	$107.92	$107.90	$107.90
7 purchase totals =	$920.78		$1,016.8663	$1,016.87	$1,016.85	$1,016.90