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	$10.45	4.408%	$10.9106	$10.91	$10.90	$10.90
Purchase #2	$152.47	13.439%	$172.9604	$172.96	$172.95	$173.00
Purchase #3	$187.69	10.649%	$207.6771	$207.68	$207.70	$207.70
Purchase #4	$152.59	13.240%	$172.7929	$172.79	$172.80	$172.80
Purchase #5	$83.67	7.327%	$89.8005	$89.80	$89.80	$89.80
Purchase #6	$138.73	8.547%	$150.5873	$150.59	$150.60	$150.60
Purchase #7	$126.43	8.257%	$136.8693	$136.87	$136.85	$136.90
7 purchase totals =	$852.03		$941.5981	$941.60	$941.60	$941.70