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	$72.49	8.308%	$78.5125	$78.51	$78.50	$78.50
Purchase #2	$68.52	11.720%	$76.5505	$76.55	$76.55	$76.60
Purchase #3	$229.41	11.276%	$255.2783	$255.28	$255.30	$255.30
Purchase #4	$184.29	5.857%	$195.0839	$195.08	$195.10	$195.10
Purchase #5	$129.45	12.469%	$145.5911	$145.59	$145.60	$145.60
Purchase #6	$218.93	6.667%	$233.5261	$233.53	$233.55	$233.50
Purchase #7	$84.87	13.275%	$96.1365	$96.14	$96.15	$96.10
7 purchase totals =	$987.96		$1,080.6789	$1,080.68	$1,080.75	$1,080.70