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	$92.38	7.624%	$99.4231	$99.42	$99.40	$99.40
Purchase #2	$100.73	13.762%	$114.5925	$114.59	$114.60	$114.60
Purchase #3	$85.70	3.195%	$88.4381	$88.44	$88.45	$88.40
Purchase #4	$22.99	12.849%	$25.944	$25.94	$25.95	$25.90
Purchase #5	$45.88	6.715%	$48.9608	$48.96	$48.95	$49.00
Purchase #6	$249.64	11.497%	$278.3411	$278.34	$278.35	$278.30
Purchase #7	$131.28	11.500%	$146.3772	$146.38	$146.40	$146.40
7 purchase totals =	$728.60		$802.0768	$802.07	$802.10	$802.00