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	$173.31	3.501%	$179.3776	$179.38	$179.40	$179.40
Purchase #2	$111.69	5.574%	$117.9156	$117.92	$117.90	$117.90
Purchase #3	$87.77	10.282%	$96.7945	$96.79	$96.80	$96.80
Purchase #4	$234.83	7.564%	$252.5925	$252.59	$252.60	$252.60
Purchase #5	$135.49	9.370%	$148.1854	$148.19	$148.20	$148.20
Purchase #6	$185.91	5.643%	$196.4009	$196.40	$196.40	$196.40
Purchase #7	$114.32	11.170%	$127.0895	$127.09	$127.10	$127.10
7 purchase totals =	$1,043.32		$1,118.3560	$1,118.36	$1,118.40	$1,118.40