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	$225.56	13.459%	$255.9181	$255.92	$255.90	$255.90
Purchase #2	$147.73	9.267%	$161.4201	$161.42	$161.40	$161.40
Purchase #3	$201.75	6.628%	$215.122	$215.12	$215.10	$215.10
Purchase #4	$142.37	6.420%	$151.5102	$151.51	$151.50	$151.50
Purchase #5	$222.57	10.152%	$245.1653	$245.17	$245.15	$245.20
Purchase #6	$43.83	3.618%	$45.4158	$45.42	$45.40	$45.40
Purchase #7	$87.72	6.842%	$93.7218	$93.72	$93.70	$93.70
7 purchase totals =	$1,071.53		$1,168.2733	$1,168.28	$1,168.15	$1,168.20