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	$150.61	5.466%	$158.8423	$158.84	$158.85	$158.80
Purchase #2	$95.84	12.587%	$107.9034	$107.90	$107.90	$107.90
Purchase #3	$208.32	4.509%	$217.7131	$217.71	$217.70	$217.70
Purchase #4	$80.63	11.397%	$89.8194	$89.82	$89.80	$89.80
Purchase #5	$142.30	11.832%	$159.1369	$159.14	$159.15	$159.10
Purchase #6	$170.31	12.139%	$190.9839	$190.98	$191.00	$191.00
Purchase #7	$205.25	11.179%	$228.1949	$228.19	$228.20	$228.20
7 purchase totals =	$1,053.26		$1,152.5939	$1,152.58	$1,152.60	$1,152.50