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	$28.51	5.418%	$30.0547	$30.05	$30.05	$30.10
Purchase #2	$209.60	13.840%	$238.6086	$238.61	$238.60	$238.60
Purchase #3	$20.53	3.540%	$21.2568	$21.26	$21.25	$21.30
Purchase #4	$12.51	12.640%	$14.0913	$14.09	$14.10	$14.10
Purchase #5	$75.42	4.117%	$78.525	$78.53	$78.55	$78.50
Purchase #6	$100.27	5.318%	$105.6024	$105.60	$105.60	$105.60
Purchase #7	$22.93	12.781%	$25.8607	$25.86	$25.85	$25.90
7 purchase totals =	$469.77		$513.9995	$514.00	$514.00	$514.10