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	$57.77	3.317%	$59.6862	$59.69	$59.70	$59.70
Purchase #2	$127.51	11.605%	$142.3075	$142.31	$142.30	$142.30
Purchase #3	$9.38	8.212%	$10.1503	$10.15	$10.15	$10.20
Purchase #4	$42.52	3.381%	$43.9576	$43.96	$43.95	$44.00
Purchase #5	$165.92	4.744%	$173.7912	$173.79	$173.80	$173.80
Purchase #6	$175.25	6.372%	$186.4169	$186.42	$186.40	$186.40
Purchase #7	$146.30	9.253%	$159.8371	$159.84	$159.85	$159.80
7 purchase totals =	$724.65		$776.1468	$776.16	$776.15	$776.20