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	$86.66	6.724%	$92.487	$92.49	$92.50	$92.50
Purchase #2	$182.83	9.609%	$200.3981	$200.40	$200.40	$200.40
Purchase #3	$35.58	5.458%	$37.522	$37.52	$37.50	$37.50
Purchase #4	$5.29	11.831%	$5.9159	$5.92	$5.90	$5.90
Purchase #5	$234.85	8.820%	$255.5638	$255.56	$255.55	$255.60
Purchase #6	$151.79	10.300%	$167.4244	$167.42	$167.40	$167.40
Purchase #7	$122.55	7.686%	$131.9692	$131.97	$131.95	$132.00
7 purchase totals =	$819.55		$891.2804	$891.28	$891.20	$891.30