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	$170.85	9.510%	$187.0978	$187.10	$187.10	$187.10
Purchase #2	$223.95	4.132%	$233.2036	$233.20	$233.20	$233.20
Purchase #3	$36.54	6.724%	$38.9969	$39.00	$39.00	$39.00
Purchase #4	$113.27	4.253%	$118.0874	$118.09	$118.10	$118.10
Purchase #5	$6.64	13.547%	$7.5395	$7.54	$7.55	$7.50
Purchase #6	$146.29	8.278%	$158.3999	$158.40	$158.40	$158.40
Purchase #7	$144.50	5.796%	$152.8752	$152.88	$152.90	$152.90
7 purchase totals =	$842.04		$896.2003	$896.21	$896.25	$896.20