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	$10.52	11.871%	$11.7688	$11.77	$11.75	$11.80
Purchase #2	$207.34	10.258%	$228.6089	$228.61	$228.60	$228.60
Purchase #3	$111.60	5.179%	$117.3798	$117.38	$117.40	$117.40
Purchase #4	$37.25	9.265%	$40.7012	$40.70	$40.70	$40.70
Purchase #5	$40.38	6.272%	$42.9126	$42.91	$42.90	$42.90
Purchase #6	$13.97	9.624%	$15.3145	$15.31	$15.30	$15.30
Purchase #7	$148.95	5.213%	$156.7148	$156.71	$156.70	$156.70
7 purchase totals =	$570.01		$613.4006	$613.39	$613.35	$613.40