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	$35.70	9.688%	$39.1586	$39.16	$39.15	$39.20
Purchase #2	$151.26	5.110%	$158.9894	$158.99	$159.00	$159.00
Purchase #3	$37.27	3.606%	$38.614	$38.61	$38.60	$38.60
Purchase #4	$224.74	9.234%	$245.4925	$245.49	$245.50	$245.50
Purchase #5	$153.64	3.410%	$158.8791	$158.88	$158.90	$158.90
Purchase #6	$42.59	4.690%	$44.5875	$44.59	$44.60	$44.60
Purchase #7	$18.69	10.759%	$20.7009	$20.70	$20.70	$20.70
7 purchase totals =	$663.89		$706.4220	$706.42	$706.45	$706.50