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	$110.86	11.353%	$123.4459	$123.45	$123.45	$123.40
Purchase #2	$47.93	10.659%	$53.0389	$53.04	$53.05	$53.00
Purchase #3	$111.85	13.844%	$127.3345	$127.33	$127.35	$127.30
Purchase #4	$19.68	4.348%	$20.5357	$20.54	$20.55	$20.50
Purchase #5	$247.98	9.419%	$271.3372	$271.34	$271.35	$271.30
Purchase #6	$20.61	3.247%	$21.2792	$21.28	$21.30	$21.30
Purchase #7	$20.82	7.758%	$22.4352	$22.44	$22.45	$22.40
7 purchase totals =	$579.73		$639.4066	$639.42	$639.50	$639.20