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	$98.80	12.530%	$111.1796	$111.18	$111.20	$111.20
Purchase #2	$48.38	8.754%	$52.6152	$52.62	$52.60	$52.60
Purchase #3	$21.98	6.250%	$23.3538	$23.35	$23.35	$23.40
Purchase #4	$86.35	3.392%	$89.279	$89.28	$89.30	$89.30
Purchase #5	$107.30	11.558%	$119.7017	$119.70	$119.70	$119.70
Purchase #6	$224.77	6.296%	$238.9215	$238.92	$238.90	$238.90
Purchase #7	$155.56	6.187%	$165.1845	$165.18	$165.20	$165.20
7 purchase totals =	$743.14		$800.2353	$800.23	$800.25	$800.30