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	$138.58	6.303%	$147.3147	$147.31	$147.30	$147.30
Purchase #2	$92.88	6.795%	$99.1912	$99.19	$99.20	$99.20
Purchase #3	$111.91	13.595%	$127.1242	$127.12	$127.10	$127.10
Purchase #4	$30.27	12.150%	$33.9478	$33.95	$33.95	$33.90
Purchase #5	$250.39	11.656%	$279.5755	$279.58	$279.60	$279.60
Purchase #6	$193.66	3.777%	$200.9745	$200.97	$200.95	$201.00
Purchase #7	$234.27	9.206%	$255.8369	$255.84	$255.85	$255.80
7 purchase totals =	$1,051.96		$1,143.9648	$1,143.96	$1,143.95	$1,143.90