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	$239.90	6.529%	$255.5631	$255.56	$255.55	$255.60
Purchase #2	$49.34	8.298%	$53.4342	$53.43	$53.45	$53.40
Purchase #3	$136.26	12.621%	$153.4574	$153.46	$153.45	$153.50
Purchase #4	$156.92	9.712%	$172.1601	$172.16	$172.15	$172.20
Purchase #5	$239.78	8.658%	$260.5402	$260.54	$260.55	$260.50
Purchase #6	$117.99	11.219%	$131.2273	$131.23	$131.25	$131.20
Purchase #7	$50.68	13.610%	$57.5775	$57.58	$57.60	$57.60
7 purchase totals =	$990.87		$1,083.9598	$1,083.96	$1,084.00	$1,084.00