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	$130.25	6.352%	$138.5235	$138.52	$138.50	$138.50
Purchase #2	$80.71	11.706%	$90.1579	$90.16	$90.15	$90.20
Purchase #3	$149.72	12.853%	$168.9635	$168.96	$168.95	$169.00
Purchase #4	$76.81	6.296%	$81.646	$81.65	$81.65	$81.60
Purchase #5	$97.47	7.808%	$105.0805	$105.08	$105.10	$105.10
Purchase #6	$102.49	4.346%	$106.9442	$106.94	$106.95	$106.90
Purchase #7	$190.52	5.210%	$200.4461	$200.45	$200.45	$200.40
7 purchase totals =	$827.97		$891.7617	$891.76	$891.75	$891.70