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	$83.50	9.183%	$91.1678	$91.17	$91.15	$91.20
Purchase #2	$121.46	5.353%	$127.9618	$127.96	$127.95	$128.00
Purchase #3	$91.66	9.352%	$100.232	$100.23	$100.25	$100.20
Purchase #4	$206.89	6.602%	$220.5489	$220.55	$220.55	$220.50
Purchase #5	$105.99	5.422%	$111.7368	$111.74	$111.75	$111.70
Purchase #6	$44.43	3.289%	$45.8913	$45.89	$45.90	$45.90
Purchase #7	$174.60	10.675%	$193.2386	$193.24	$193.25	$193.20
7 purchase totals =	$828.53		$890.7772	$890.78	$890.80	$890.70