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	$155.29	11.352%	$172.9185	$172.92	$172.90	$172.90
Purchase #2	$218.91	9.501%	$239.7086	$239.71	$239.70	$239.70
Purchase #3	$239.54	6.257%	$254.528	$254.53	$254.55	$254.50
Purchase #4	$33.90	11.152%	$37.6805	$37.68	$37.70	$37.70
Purchase #5	$12.61	7.789%	$13.5922	$13.59	$13.60	$13.60
Purchase #6	$122.50	4.332%	$127.8067	$127.81	$127.80	$127.80
Purchase #7	$87.61	9.397%	$95.8427	$95.84	$95.85	$95.80
7 purchase totals =	$870.36		$942.0772	$942.08	$942.10	$942.00