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	$167.88	12.506%	$188.8751	$188.88	$188.90	$188.90
Purchase #2	$219.58	6.379%	$233.587	$233.59	$233.60	$233.60
Purchase #3	$127.95	13.388%	$145.0799	$145.08	$145.10	$145.10
Purchase #4	$50.44	6.212%	$53.5733	$53.57	$53.55	$53.60
Purchase #5	$127.84	11.352%	$142.3524	$142.35	$142.35	$142.40
Purchase #6	$11.35	9.232%	$12.3978	$12.40	$12.40	$12.40
Purchase #7	$48.49	9.103%	$52.904	$52.90	$52.90	$52.90
7 purchase totals =	$753.53		$828.7695	$828.77	$828.80	$828.90