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	$229.58	5.608%	$242.4548	$242.45	$242.45	$242.50
Purchase #2	$215.84	11.796%	$241.3005	$241.30	$241.30	$241.30
Purchase #3	$166.90	8.105%	$180.4272	$180.43	$180.45	$180.40
Purchase #4	$99.61	10.826%	$110.3938	$110.39	$110.40	$110.40
Purchase #5	$123.31	3.509%	$127.6369	$127.64	$127.65	$127.60
Purchase #6	$205.84	5.141%	$216.4222	$216.42	$216.40	$216.40
Purchase #7	$153.52	11.270%	$170.8217	$170.82	$170.80	$170.80
7 purchase totals =	$1,194.60		$1,289.4571	$1,289.45	$1,289.45	$1,289.40