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	$23.86	11.514%	$26.6072	$26.61	$26.60	$26.60
Purchase #2	$96.89	8.473%	$105.0995	$105.10	$105.10	$105.10
Purchase #3	$56.83	4.600%	$59.4442	$59.44	$59.45	$59.40
Purchase #4	$126.50	4.662%	$132.3974	$132.40	$132.40	$132.40
Purchase #5	$44.60	13.392%	$50.5728	$50.57	$50.55	$50.60
Purchase #6	$138.28	6.110%	$146.7289	$146.73	$146.75	$146.70
Purchase #7	$161.34	4.845%	$169.1569	$169.16	$169.15	$169.20
7 purchase totals =	$648.30		$690.0069	$690.01	$690.00	$690.00