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	$21.51	3.487%	$22.2601	$22.26	$22.25	$22.30
Purchase #2	$111.80	7.530%	$120.2185	$120.22	$120.20	$120.20
Purchase #3	$95.37	10.592%	$105.4716	$105.47	$105.45	$105.50
Purchase #4	$35.67	5.412%	$37.6005	$37.60	$37.60	$37.60
Purchase #5	$73.36	11.196%	$81.5734	$81.57	$81.55	$81.60
Purchase #6	$135.39	12.113%	$151.7898	$151.79	$151.80	$151.80
Purchase #7	$213.61	4.246%	$222.6799	$222.68	$222.70	$222.70
7 purchase totals =	$686.71		$741.5938	$741.59	$741.55	$741.70