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	$98.29	13.345%	$111.4068	$111.41	$111.40	$111.40
Purchase #2	$75.52	9.105%	$82.3961	$82.40	$82.40	$82.40
Purchase #3	$228.99	11.522%	$255.3742	$255.37	$255.35	$255.40
Purchase #4	$183.64	9.421%	$200.9407	$200.94	$200.95	$200.90
Purchase #5	$46.93	11.309%	$52.2373	$52.24	$52.25	$52.20
Purchase #6	$74.95	7.107%	$80.2767	$80.28	$80.30	$80.30
Purchase #7	$65.31	13.560%	$74.166	$74.17	$74.15	$74.20
7 purchase totals =	$773.63		$856.7978	$856.81	$856.80	$856.80