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	$8.33	7.640%	$8.9664	$8.97	$8.95	$9.00
Purchase #2	$161.28	13.726%	$183.4173	$183.42	$183.40	$183.40
Purchase #3	$167.86	11.581%	$187.2999	$187.30	$187.30	$187.30
Purchase #4	$166.53	10.407%	$183.8608	$183.86	$183.85	$183.90
Purchase #5	$89.79	9.784%	$98.5751	$98.58	$98.60	$98.60
Purchase #6	$100.87	4.432%	$105.3406	$105.34	$105.35	$105.30
Purchase #7	$209.59	6.134%	$222.4463	$222.45	$222.45	$222.40
7 purchase totals =	$904.25		$989.9064	$989.92	$989.90	$989.90