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	$111.52	6.255%	$118.4956	$118.50	$118.50	$118.50
Purchase #2	$159.32	8.166%	$172.3301	$172.33	$172.35	$172.30
Purchase #3	$118.56	10.408%	$130.8997	$130.90	$130.90	$130.90
Purchase #4	$70.68	6.314%	$75.1427	$75.14	$75.15	$75.10
Purchase #5	$150.61	6.324%	$160.1346	$160.13	$160.15	$160.10
Purchase #6	$180.73	4.446%	$188.7653	$188.77	$188.75	$188.80
Purchase #7	$38.86	5.347%	$40.9378	$40.94	$40.95	$40.90
7 purchase totals =	$830.28		$886.7058	$886.71	$886.75	$886.60