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	$167.76	6.155%	$178.0856	$178.09	$178.10	$178.10
Purchase #2	$158.99	11.254%	$176.8827	$176.88	$176.90	$176.90
Purchase #3	$224.48	4.160%	$233.8184	$233.82	$233.80	$233.80
Purchase #4	$35.49	12.306%	$39.8574	$39.86	$39.85	$39.90
Purchase #5	$134.51	7.815%	$145.022	$145.02	$145.00	$145.00
Purchase #6	$40.59	5.333%	$42.7547	$42.75	$42.75	$42.80
Purchase #7	$131.30	10.749%	$145.4134	$145.41	$145.40	$145.40
7 purchase totals =	$893.12		$961.8342	$961.83	$961.80	$961.90