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	$52.32	13.867%	$59.5752	$59.58	$59.60	$59.60
Purchase #2	$133.68	13.366%	$151.5477	$151.55	$151.55	$151.50
Purchase #3	$95.55	4.441%	$99.7934	$99.79	$99.80	$99.80
Purchase #4	$10.87	11.153%	$12.0823	$12.08	$12.10	$12.10
Purchase #5	$205.87	4.172%	$214.4589	$214.46	$214.45	$214.50
Purchase #6	$150.65	11.321%	$167.7051	$167.71	$167.70	$167.70
Purchase #7	$121.83	5.843%	$128.9485	$128.95	$128.95	$128.90
7 purchase totals =	$770.77		$834.1111	$834.12	$834.15	$834.10