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	$22.87	6.419%	$24.338	$24.34	$24.35	$24.30
Purchase #2	$178.77	3.506%	$185.0377	$185.04	$185.05	$185.00
Purchase #3	$51.34	4.255%	$53.5245	$53.52	$53.50	$53.50
Purchase #4	$199.59	6.466%	$212.4955	$212.50	$212.50	$212.50
Purchase #5	$89.44	12.103%	$100.2649	$100.26	$100.25	$100.30
Purchase #6	$218.50	10.395%	$241.2131	$241.21	$241.20	$241.20
Purchase #7	$41.71	6.623%	$44.4725	$44.47	$44.45	$44.50
7 purchase totals =	$802.22		$861.3462	$861.34	$861.30	$861.30