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	$25.89	8.611%	$28.1194	$28.12	$28.10	$28.10
Purchase #2	$18.52	11.573%	$20.6633	$20.66	$20.65	$20.70
Purchase #3	$128.42	12.362%	$144.2953	$144.30	$144.30	$144.30
Purchase #4	$120.37	10.147%	$132.5839	$132.58	$132.60	$132.60
Purchase #5	$142.37	11.513%	$158.7611	$158.76	$158.75	$158.80
Purchase #6	$43.37	10.708%	$48.0141	$48.01	$48.00	$48.00
Purchase #7	$145.77	7.432%	$156.6036	$156.60	$156.60	$156.60
7 purchase totals =	$624.71		$689.0407	$689.03	$689.00	$689.10