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	$103.76	7.447%	$111.487	$111.49	$111.50	$111.50
Purchase #2	$110.39	5.817%	$116.8114	$116.81	$116.80	$116.80
Purchase #3	$78.70	13.491%	$89.3174	$89.32	$89.30	$89.30
Purchase #4	$183.50	4.493%	$191.7447	$191.74	$191.75	$191.70
Purchase #5	$123.77	10.496%	$136.7609	$136.76	$136.75	$136.80
Purchase #6	$210.66	11.440%	$234.7595	$234.76	$234.75	$234.80
Purchase #7	$241.60	11.779%	$270.0581	$270.06	$270.05	$270.10
7 purchase totals =	$1,052.38		$1,150.9390	$1,150.94	$1,150.90	$1,151.00