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	$172.56	8.305%	$186.8911	$186.89	$186.90	$186.90
Purchase #2	$21.83	12.248%	$24.5037	$24.50	$24.50	$24.50
Purchase #3	$74.44	6.687%	$79.4178	$79.42	$79.40	$79.40
Purchase #4	$132.35	11.273%	$147.2698	$147.27	$147.25	$147.30
Purchase #5	$21.60	4.512%	$22.5746	$22.57	$22.55	$22.60
Purchase #6	$85.59	5.840%	$90.5885	$90.59	$90.60	$90.60
Purchase #7	$20.94	4.792%	$21.9434	$21.94	$21.95	$21.90
7 purchase totals =	$529.31		$573.1889	$573.18	$573.15	$573.20