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	$229.72	13.202%	$260.0476	$260.05	$260.05	$260.00
Purchase #2	$52.81	4.759%	$55.3232	$55.32	$55.30	$55.30
Purchase #3	$240.95	13.768%	$274.124	$274.12	$274.10	$274.10
Purchase #4	$65.55	9.412%	$71.7196	$71.72	$71.70	$71.70
Purchase #5	$155.89	6.571%	$166.1335	$166.13	$166.15	$166.10
Purchase #6	$82.93	9.468%	$90.7818	$90.78	$90.80	$90.80
Purchase #7	$227.38	5.712%	$240.3679	$240.37	$240.35	$240.40
7 purchase totals =	$1,055.23		$1,158.4976	$1,158.49	$1,158.45	$1,158.40