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	$19.27	10.641%	$21.3205	$21.32	$21.30	$21.30
Purchase #2	$88.36	4.782%	$92.5854	$92.59	$92.60	$92.60
Purchase #3	$242.68	5.412%	$255.8138	$255.81	$255.80	$255.80
Purchase #4	$164.74	13.152%	$186.4066	$186.41	$186.40	$186.40
Purchase #5	$83.29	6.179%	$88.4365	$88.44	$88.45	$88.40
Purchase #6	$38.29	5.636%	$40.448	$40.45	$40.45	$40.40
Purchase #7	$81.30	11.571%	$90.7072	$90.71	$90.70	$90.70
7 purchase totals =	$717.93		$775.7180	$775.73	$775.70	$775.60