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	$153.87	10.621%	$170.2125	$170.21	$170.20	$170.20
Purchase #2	$80.80	5.608%	$85.3313	$85.33	$85.35	$85.30
Purchase #3	$146.25	4.194%	$152.3837	$152.38	$152.40	$152.40
Purchase #4	$205.69	13.610%	$233.6844	$233.68	$233.70	$233.70
Purchase #5	$50.96	3.141%	$52.5607	$52.56	$52.55	$52.60
Purchase #6	$241.96	13.841%	$275.4497	$275.45	$275.45	$275.40
Purchase #7	$116.47	11.742%	$130.1459	$130.15	$130.15	$130.10
7 purchase totals =	$996.00		$1,099.7682	$1,099.76	$1,099.80	$1,099.70