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	$91.72	9.535%	$100.4655	$100.47	$100.45	$100.50
Purchase #2	$127.79	11.645%	$142.6711	$142.67	$142.65	$142.70
Purchase #3	$180.63	6.176%	$191.7857	$191.79	$191.80	$191.80
Purchase #4	$152.62	7.871%	$164.6327	$164.63	$164.65	$164.60
Purchase #5	$66.91	10.631%	$74.0232	$74.02	$74.00	$74.00
Purchase #6	$106.95	7.672%	$115.1552	$115.16	$115.15	$115.20
Purchase #7	$204.81	12.523%	$230.4584	$230.46	$230.45	$230.50
7 purchase totals =	$931.43		$1,019.1918	$1,019.20	$1,019.15	$1,019.30