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	$38.92	12.353%	$43.7278	$43.73	$43.75	$43.70
Purchase #2	$96.68	11.213%	$107.5207	$107.52	$107.50	$107.50
Purchase #3	$81.83	9.810%	$89.8575	$89.86	$89.85	$89.90
Purchase #4	$34.57	4.466%	$36.1139	$36.11	$36.10	$36.10
Purchase #5	$84.62	8.537%	$91.844	$91.84	$91.85	$91.80
Purchase #6	$138.99	9.583%	$152.3094	$152.31	$152.30	$152.30
Purchase #7	$62.52	13.805%	$71.1509	$71.15	$71.15	$71.20
7 purchase totals =	$538.13		$592.5242	$592.52	$592.50	$592.50