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	$78.35	4.782%	$82.0967	$82.10	$82.10	$82.10
Purchase #2	$70.53	5.257%	$74.2378	$74.24	$74.25	$74.20
Purchase #3	$100.91	10.301%	$111.3047	$111.30	$111.30	$111.30
Purchase #4	$155.86	5.283%	$164.0941	$164.09	$164.10	$164.10
Purchase #5	$241.36	3.414%	$249.6	$249.60	$249.60	$249.60
Purchase #6	$46.58	12.137%	$52.2334	$52.23	$52.25	$52.20
Purchase #7	$70.81	10.743%	$78.4171	$78.42	$78.40	$78.40
7 purchase totals =	$764.40		$811.9838	$811.98	$812.00	$811.90