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	$108.91	10.797%	$120.669	$120.67	$120.65	$120.70
Purchase #2	$108.60	13.680%	$123.4565	$123.46	$123.45	$123.50
Purchase #3	$213.74	5.321%	$225.1131	$225.11	$225.10	$225.10
Purchase #4	$238.53	10.716%	$264.0909	$264.09	$264.10	$264.10
Purchase #5	$73.75	5.669%	$77.9309	$77.93	$77.95	$77.90
Purchase #6	$186.72	3.256%	$192.7996	$192.80	$192.80	$192.80
Purchase #7	$14.32	10.834%	$15.8714	$15.87	$15.85	$15.90
7 purchase totals =	$944.57		$1,019.9314	$1,019.93	$1,019.90	$1,020.00