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	$26.69	7.589%	$28.7155	$28.72	$28.70	$28.70
Purchase #2	$48.26	11.574%	$53.8456	$53.85	$53.85	$53.80
Purchase #3	$80.27	11.124%	$89.1992	$89.20	$89.20	$89.20
Purchase #4	$102.25	4.336%	$106.6836	$106.68	$106.70	$106.70
Purchase #5	$237.53	5.472%	$250.5276	$250.53	$250.55	$250.50
Purchase #6	$40.94	13.472%	$46.4554	$46.46	$46.45	$46.50
Purchase #7	$147.49	8.784%	$160.4455	$160.45	$160.45	$160.40
7 purchase totals =	$683.43		$735.8724	$735.89	$735.90	$735.80