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	$134.92	3.699%	$139.9107	$139.91	$139.90	$139.90
Purchase #2	$95.63	8.416%	$103.6782	$103.68	$103.70	$103.70
Purchase #3	$203.36	13.404%	$230.6184	$230.62	$230.60	$230.60
Purchase #4	$238.45	13.849%	$271.4729	$271.47	$271.45	$271.50
Purchase #5	$159.30	11.872%	$178.2121	$178.21	$178.20	$178.20
Purchase #6	$48.82	5.797%	$51.6501	$51.65	$51.65	$51.70
Purchase #7	$158.72	6.165%	$168.5051	$168.51	$168.50	$168.50
7 purchase totals =	$1,039.20		$1,144.0475	$1,144.05	$1,144.00	$1,144.10