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	$41.60	11.759%	$46.4917	$46.49	$46.50	$46.50
Purchase #2	$52.83	6.307%	$56.162	$56.16	$56.15	$56.20
Purchase #3	$171.71	10.691%	$190.0675	$190.07	$190.05	$190.10
Purchase #4	$78.90	13.194%	$89.3101	$89.31	$89.30	$89.30
Purchase #5	$211.80	6.280%	$225.101	$225.10	$225.10	$225.10
Purchase #6	$218.30	11.205%	$242.7605	$242.76	$242.75	$242.80
Purchase #7	$133.77	11.775%	$149.5214	$149.52	$149.50	$149.50
7 purchase totals =	$908.91		$999.4142	$999.41	$999.35	$999.50