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	$145.57	10.630%	$161.0441	$161.04	$161.05	$161.00
Purchase #2	$97.86	5.645%	$103.3842	$103.38	$103.40	$103.40
Purchase #3	$130.94	5.481%	$138.1168	$138.12	$138.10	$138.10
Purchase #4	$98.87	13.222%	$111.9426	$111.94	$111.95	$111.90
Purchase #5	$105.73	12.235%	$118.6661	$118.67	$118.65	$118.70
Purchase #6	$155.35	11.227%	$172.7911	$172.79	$172.80	$172.80
Purchase #7	$68.72	13.721%	$78.1491	$78.15	$78.15	$78.10
7 purchase totals =	$803.04		$884.0940	$884.09	$884.10	$884.00