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	$17.27	12.171%	$19.3719	$19.37	$19.35	$19.40
Purchase #2	$214.85	3.317%	$221.9766	$221.98	$222.00	$222.00
Purchase #3	$71.59	12.567%	$80.5867	$80.59	$80.60	$80.60
Purchase #4	$116.62	8.292%	$126.2901	$126.29	$126.30	$126.30
Purchase #5	$119.55	3.585%	$123.8359	$123.84	$123.85	$123.80
Purchase #6	$155.56	6.396%	$165.5096	$165.51	$165.50	$165.50
Purchase #7	$114.28	4.105%	$118.9712	$118.97	$118.95	$119.00
7 purchase totals =	$809.72		$856.5420	$856.55	$856.55	$856.60