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	$242.60	3.118%	$250.1643	$250.16	$250.15	$250.20
Purchase #2	$104.55	6.346%	$111.1847	$111.18	$111.20	$111.20
Purchase #3	$68.27	6.166%	$72.4795	$72.48	$72.50	$72.50
Purchase #4	$110.57	7.259%	$118.5963	$118.60	$118.60	$118.60
Purchase #5	$225.55	9.683%	$247.39	$247.39	$247.40	$247.40
Purchase #6	$102.63	10.163%	$113.0603	$113.06	$113.05	$113.10
Purchase #7	$19.69	10.325%	$21.723	$21.72	$21.70	$21.70
7 purchase totals =	$873.86		$934.5981	$934.59	$934.60	$934.70