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	$59.77	12.386%	$67.1731	$67.17	$67.15	$67.20
Purchase #2	$194.80	8.556%	$211.4671	$211.47	$211.45	$211.50
Purchase #3	$245.67	10.482%	$271.4211	$271.42	$271.40	$271.40
Purchase #4	$128.79	11.228%	$143.2505	$143.25	$143.25	$143.30
Purchase #5	$138.37	4.695%	$144.8665	$144.87	$144.85	$144.90
Purchase #6	$126.67	4.698%	$132.621	$132.62	$132.60	$132.60
Purchase #7	$240.59	12.451%	$270.5459	$270.55	$270.55	$270.50
7 purchase totals =	$1,134.66		$1,241.3452	$1,241.35	$1,241.25	$1,241.40