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	$235.44	6.674%	$251.1533	$251.15	$251.15	$251.20
Purchase #2	$138.91	12.142%	$155.7765	$155.78	$155.80	$155.80
Purchase #3	$5.42	11.401%	$6.0379	$6.04	$6.05	$6.00
Purchase #4	$84.84	6.826%	$90.6312	$90.63	$90.65	$90.60
Purchase #5	$187.26	11.479%	$208.7556	$208.76	$208.75	$208.80
Purchase #6	$244.86	12.852%	$276.3294	$276.33	$276.35	$276.30
Purchase #7	$127.60	11.539%	$142.3238	$142.32	$142.30	$142.30
7 purchase totals =	$1,024.33		$1,131.0077	$1,131.01	$1,131.05	$1,131.00