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	$67.86	3.617%	$70.3145	$70.31	$70.30	$70.30
Purchase #2	$67.64	9.396%	$73.9955	$74.00	$74.00	$74.00
Purchase #3	$68.36	6.230%	$72.6188	$72.62	$72.60	$72.60
Purchase #4	$205.45	13.602%	$233.3953	$233.40	$233.40	$233.40
Purchase #5	$166.42	11.720%	$185.9244	$185.92	$185.90	$185.90
Purchase #6	$79.86	13.326%	$90.5021	$90.50	$90.50	$90.50
Purchase #7	$234.43	11.690%	$261.8349	$261.83	$261.85	$261.80
7 purchase totals =	$890.02		$988.5855	$988.58	$988.55	$988.50