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	$154.56	9.707%	$169.5631	$169.56	$169.55	$169.60
Purchase #2	$208.83	4.488%	$218.2023	$218.20	$218.20	$218.20
Purchase #3	$112.35	13.562%	$127.5869	$127.59	$127.60	$127.60
Purchase #4	$136.49	12.111%	$153.0203	$153.02	$153.00	$153.00
Purchase #5	$61.61	9.813%	$67.6558	$67.66	$67.65	$67.70
Purchase #6	$177.32	10.152%	$195.3215	$195.32	$195.30	$195.30
Purchase #7	$49.28	6.734%	$52.5985	$52.60	$52.60	$52.60
7 purchase totals =	$900.44		$983.9484	$983.95	$983.90	$984.00