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	$99.49	6.342%	$105.7997	$105.80	$105.80	$105.80
Purchase #2	$31.60	13.612%	$35.9014	$35.90	$35.90	$35.90
Purchase #3	$73.38	7.251%	$78.7008	$78.70	$78.70	$78.70
Purchase #4	$34.98	13.588%	$39.7331	$39.73	$39.75	$39.70
Purchase #5	$246.79	10.558%	$272.8461	$272.85	$272.85	$272.80
Purchase #6	$175.71	5.226%	$184.8926	$184.89	$184.90	$184.90
Purchase #7	$51.44	11.160%	$57.1807	$57.18	$57.20	$57.20
7 purchase totals =	$713.39		$775.0544	$775.05	$775.10	$775.00