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	$39.76	7.329%	$42.674	$42.67	$42.65	$42.70
Purchase #2	$87.36	9.342%	$95.5212	$95.52	$95.50	$95.50
Purchase #3	$165.49	4.117%	$172.3032	$172.30	$172.30	$172.30
Purchase #4	$49.49	5.652%	$52.2872	$52.29	$52.30	$52.30
Purchase #5	$105.56	3.748%	$109.5164	$109.52	$109.50	$109.50
Purchase #6	$155.80	8.715%	$169.378	$169.38	$169.40	$169.40
Purchase #7	$42.79	9.321%	$46.7785	$46.78	$46.80	$46.80
7 purchase totals =	$646.25		$688.4585	$688.46	$688.45	$688.50