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	$21.45	9.474%	$23.4822	$23.48	$23.50	$23.50
Purchase #2	$72.83	6.422%	$77.5071	$77.51	$77.50	$77.50
Purchase #3	$127.80	3.405%	$132.1516	$132.15	$132.15	$132.20
Purchase #4	$135.59	8.296%	$146.8385	$146.84	$146.85	$146.80
Purchase #5	$74.82	11.744%	$83.6069	$83.61	$83.60	$83.60
Purchase #6	$9.86	7.401%	$10.5897	$10.59	$10.60	$10.60
Purchase #7	$73.99	4.413%	$77.2552	$77.26	$77.25	$77.30
7 purchase totals =	$516.34		$551.4312	$551.44	$551.45	$551.50