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	$133.52	4.382%	$139.3708	$139.37	$139.35	$139.40
Purchase #2	$152.41	10.871%	$168.9785	$168.98	$169.00	$169.00
Purchase #3	$180.75	8.563%	$196.2276	$196.23	$196.25	$196.20
Purchase #4	$7.77	10.764%	$8.6064	$8.61	$8.60	$8.60
Purchase #5	$161.38	9.296%	$176.3819	$176.38	$176.40	$176.40
Purchase #6	$29.55	9.702%	$32.4169	$32.42	$32.40	$32.40
Purchase #7	$66.56	12.650%	$74.9798	$74.98	$75.00	$75.00
7 purchase totals =	$731.94		$796.9619	$796.97	$797.00	$797.00