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	$125.45	13.812%	$142.7772	$142.78	$142.80	$142.80
Purchase #2	$249.74	6.490%	$265.9481	$265.95	$265.95	$265.90
Purchase #3	$90.94	13.387%	$103.1141	$103.11	$103.10	$103.10
Purchase #4	$22.71	6.313%	$24.1437	$24.14	$24.15	$24.10
Purchase #5	$36.82	4.622%	$38.5218	$38.52	$38.50	$38.50
Purchase #6	$166.56	10.723%	$184.4202	$184.42	$184.40	$184.40
Purchase #7	$223.81	6.446%	$238.2368	$238.24	$238.25	$238.20
7 purchase totals =	$916.03		$997.1619	$997.16	$997.15	$997.00