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	$127.86	8.121%	$138.2435	$138.24	$138.25	$138.20
Purchase #2	$123.63	3.224%	$127.6158	$127.62	$127.60	$127.60
Purchase #3	$99.98	5.379%	$105.3579	$105.36	$105.35	$105.40
Purchase #4	$104.54	4.247%	$108.9798	$108.98	$109.00	$109.00
Purchase #5	$173.70	9.608%	$190.3891	$190.39	$190.40	$190.40
Purchase #6	$28.72	9.409%	$31.4223	$31.42	$31.40	$31.40
Purchase #7	$54.78	9.330%	$59.891	$59.89	$59.90	$59.90
7 purchase totals =	$713.21		$761.8994	$761.90	$761.90	$761.90