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	$123.36	13.493%	$140.005	$140.01	$140.00	$140.00
Purchase #2	$32.30	6.174%	$34.2942	$34.29	$34.30	$34.30
Purchase #3	$183.72	13.303%	$208.1603	$208.16	$208.15	$208.20
Purchase #4	$37.30	8.827%	$40.5925	$40.59	$40.60	$40.60
Purchase #5	$22.93	6.187%	$24.3487	$24.35	$24.35	$24.30
Purchase #6	$57.56	6.640%	$61.382	$61.38	$61.40	$61.40
Purchase #7	$136.71	6.108%	$145.0602	$145.06	$145.05	$145.10
7 purchase totals =	$593.88		$653.8429	$653.84	$653.85	$653.90