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	$156.42	6.511%	$166.6045	$166.60	$166.60	$166.60
Purchase #2	$194.84	12.345%	$218.893	$218.89	$218.90	$218.90
Purchase #3	$167.77	3.511%	$173.6604	$173.66	$173.65	$173.70
Purchase #4	$86.49	3.651%	$89.6477	$89.65	$89.65	$89.60
Purchase #5	$87.83	3.381%	$90.7995	$90.80	$90.80	$90.80
Purchase #6	$153.28	3.472%	$158.6019	$158.60	$158.60	$158.60
Purchase #7	$97.90	13.724%	$111.3358	$111.34	$111.35	$111.30
7 purchase totals =	$944.53		$1,009.5428	$1,009.54	$1,009.55	$1,009.50