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	$53.85	10.167%	$59.3249	$59.32	$59.30	$59.30
Purchase #2	$92.50	10.318%	$102.0442	$102.04	$102.05	$102.00
Purchase #3	$31.46	6.341%	$33.4549	$33.45	$33.45	$33.50
Purchase #4	$244.86	4.534%	$255.962	$255.96	$255.95	$256.00
Purchase #5	$31.25	9.587%	$34.2459	$34.25	$34.25	$34.20
Purchase #6	$68.95	3.279%	$71.2109	$71.21	$71.20	$71.20
Purchase #7	$80.38	3.735%	$83.3822	$83.38	$83.40	$83.40
7 purchase totals =	$603.25		$639.6250	$639.61	$639.60	$639.60