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	$146.65	5.841%	$155.2158	$155.22	$155.20	$155.20
Purchase #2	$202.29	10.107%	$222.7355	$222.74	$222.75	$222.70
Purchase #3	$172.61	4.634%	$180.6087	$180.61	$180.60	$180.60
Purchase #4	$225.97	13.194%	$255.7845	$255.78	$255.80	$255.80
Purchase #5	$187.53	11.825%	$209.7054	$209.71	$209.70	$209.70
Purchase #6	$7.65	6.545%	$8.1507	$8.15	$8.15	$8.20
Purchase #7	$123.65	3.456%	$127.9233	$127.92	$127.90	$127.90
7 purchase totals =	$1,066.35		$1,160.1239	$1,160.13	$1,160.10	$1,160.10