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	$131.88	5.608%	$139.2758	$139.28	$139.30	$139.30
Purchase #2	$132.26	9.243%	$144.4848	$144.48	$144.50	$144.50
Purchase #3	$169.68	10.796%	$187.9987	$188.00	$188.00	$188.00
Purchase #4	$250.97	11.474%	$279.7663	$279.77	$279.75	$279.80
Purchase #5	$9.42	10.281%	$10.3885	$10.39	$10.40	$10.40
Purchase #6	$79.56	13.305%	$90.1455	$90.15	$90.15	$90.10
Purchase #7	$205.49	6.825%	$219.5147	$219.51	$219.50	$219.50
7 purchase totals =	$979.26		$1,071.5743	$1,071.58	$1,071.60	$1,071.60