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	$159.31	12.729%	$179.5886	$179.59	$179.60	$179.60
Purchase #2	$114.91	8.733%	$124.9451	$124.95	$124.95	$124.90
Purchase #3	$95.86	9.517%	$104.983	$104.98	$105.00	$105.00
Purchase #4	$220.40	13.115%	$249.3055	$249.31	$249.30	$249.30
Purchase #5	$82.61	4.615%	$86.4225	$86.42	$86.40	$86.40
Purchase #6	$11.81	6.766%	$12.6091	$12.61	$12.60	$12.60
Purchase #7	$90.27	5.408%	$95.1518	$95.15	$95.15	$95.20
7 purchase totals =	$775.17		$853.0056	$853.01	$853.00	$853.00