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	$150.59	11.845%	$168.4274	$168.43	$168.45	$168.40
Purchase #2	$244.79	12.127%	$274.4757	$274.48	$274.50	$274.50
Purchase #3	$88.70	11.639%	$99.0238	$99.02	$99.00	$99.00
Purchase #4	$114.52	10.348%	$126.3705	$126.37	$126.35	$126.40
Purchase #5	$141.28	3.776%	$146.6147	$146.61	$146.60	$146.60
Purchase #6	$226.69	12.695%	$255.4683	$255.47	$255.45	$255.50
Purchase #7	$179.27	9.451%	$196.2128	$196.21	$196.20	$196.20
7 purchase totals =	$1,145.84		$1,266.5932	$1,266.59	$1,266.55	$1,266.60