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	$79.59	3.497%	$82.3733	$82.37	$82.35	$82.40
Purchase #2	$166.51	13.553%	$189.0771	$189.08	$189.10	$189.10
Purchase #3	$145.77	4.466%	$152.2801	$152.28	$152.30	$152.30
Purchase #4	$133.33	13.397%	$151.1922	$151.19	$151.20	$151.20
Purchase #5	$88.96	12.233%	$99.8425	$99.84	$99.85	$99.80
Purchase #6	$247.29	12.351%	$277.8328	$277.83	$277.85	$277.80
Purchase #7	$58.40	7.226%	$62.62	$62.62	$62.60	$62.60
7 purchase totals =	$919.85		$1,015.2180	$1,015.21	$1,015.25	$1,015.20