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	$172.65	7.257%	$185.1792	$185.18	$185.20	$185.20
Purchase #2	$180.81	8.765%	$196.658	$196.66	$196.65	$196.70
Purchase #3	$178.29	5.422%	$187.9569	$187.96	$187.95	$188.00
Purchase #4	$97.25	12.618%	$109.521	$109.52	$109.50	$109.50
Purchase #5	$14.74	5.318%	$15.5239	$15.52	$15.50	$15.50
Purchase #6	$149.84	7.115%	$160.5011	$160.50	$160.50	$160.50
Purchase #7	$47.92	10.725%	$53.0594	$53.06	$53.05	$53.10
7 purchase totals =	$841.50		$908.3995	$908.40	$908.35	$908.50