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	$58.98	13.560%	$66.9777	$66.98	$67.00	$67.00
Purchase #2	$153.32	9.872%	$168.4558	$168.46	$168.45	$168.50
Purchase #3	$43.27	5.586%	$45.6871	$45.69	$45.70	$45.70
Purchase #4	$156.83	6.223%	$166.5895	$166.59	$166.60	$166.60
Purchase #5	$77.58	4.721%	$81.2426	$81.24	$81.25	$81.20
Purchase #6	$95.83	13.108%	$108.3914	$108.39	$108.40	$108.40
Purchase #7	$28.97	5.703%	$30.6222	$30.62	$30.60	$30.60
7 purchase totals =	$614.78		$667.9663	$667.97	$668.00	$668.00