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	$17.82	10.190%	$19.6359	$19.64	$19.65	$19.60
Purchase #2	$107.66	10.379%	$118.834	$118.83	$118.85	$118.80
Purchase #3	$208.39	10.811%	$230.919	$230.92	$230.90	$230.90
Purchase #4	$131.32	11.606%	$146.561	$146.56	$146.55	$146.60
Purchase #5	$198.40	8.598%	$215.4584	$215.46	$215.45	$215.50
Purchase #6	$167.65	6.413%	$178.4014	$178.40	$178.40	$178.40
Purchase #7	$242.35	6.839%	$258.9243	$258.92	$258.90	$258.90
7 purchase totals =	$1,073.59		$1,168.7340	$1,168.73	$1,168.70	$1,168.70