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	$6.97	10.699%	$7.7157	$7.72	$7.70	$7.70
Purchase #2	$205.56	11.611%	$229.4276	$229.43	$229.45	$229.40
Purchase #3	$117.28	8.728%	$127.5162	$127.52	$127.50	$127.50
Purchase #4	$118.98	10.204%	$131.1207	$131.12	$131.10	$131.10
Purchase #5	$72.32	10.193%	$79.6916	$79.69	$79.70	$79.70
Purchase #6	$140.57	10.559%	$155.4128	$155.41	$155.40	$155.40
Purchase #7	$84.25	5.325%	$88.7363	$88.74	$88.75	$88.70
7 purchase totals =	$745.93		$819.6209	$819.63	$819.60	$819.50