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	$16.65	13.115%	$18.8336	$18.83	$18.85	$18.80
Purchase #2	$92.35	9.155%	$100.8046	$100.80	$100.80	$100.80
Purchase #3	$247.36	6.169%	$262.6196	$262.62	$262.60	$262.60
Purchase #4	$153.79	11.593%	$171.6189	$171.62	$171.60	$171.60
Purchase #5	$98.69	6.638%	$105.241	$105.24	$105.25	$105.20
Purchase #6	$95.85	3.845%	$99.5354	$99.54	$99.55	$99.50
Purchase #7	$113.64	13.630%	$129.1291	$129.13	$129.15	$129.10
7 purchase totals =	$818.33		$887.7822	$887.78	$887.80	$887.60