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	$69.31	13.533%	$78.6897	$78.69	$78.70	$78.70
Purchase #2	$123.41	4.370%	$128.803	$128.80	$128.80	$128.80
Purchase #3	$34.97	12.186%	$39.2314	$39.23	$39.25	$39.20
Purchase #4	$67.44	7.799%	$72.6996	$72.70	$72.70	$72.70
Purchase #5	$229.89	10.745%	$254.5917	$254.59	$254.60	$254.60
Purchase #6	$9.98	7.240%	$10.7026	$10.70	$10.70	$10.70
Purchase #7	$114.91	11.391%	$127.9994	$128.00	$128.00	$128.00
7 purchase totals =	$649.91		$712.7174	$712.71	$712.75	$712.70