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	$19.60	5.186%	$20.6165	$20.62	$20.60	$20.60
Purchase #2	$139.90	3.538%	$144.8497	$144.85	$144.85	$144.80
Purchase #3	$46.75	11.480%	$52.1169	$52.12	$52.10	$52.10
Purchase #4	$167.48	3.839%	$173.9096	$173.91	$173.90	$173.90
Purchase #5	$55.90	10.572%	$61.8097	$61.81	$61.80	$61.80
Purchase #6	$8.77	10.409%	$9.6829	$9.68	$9.70	$9.70
Purchase #7	$30.61	8.869%	$33.3248	$33.32	$33.30	$33.30
7 purchase totals =	$469.01		$496.3101	$496.31	$496.25	$496.20