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	$80.79	9.688%	$88.6169	$88.62	$88.60	$88.60
Purchase #2	$71.52	11.526%	$79.7634	$79.76	$79.75	$79.80
Purchase #3	$123.75	5.657%	$130.7505	$130.75	$130.75	$130.80
Purchase #4	$83.45	7.757%	$89.9232	$89.92	$89.90	$89.90
Purchase #5	$149.51	12.334%	$167.9506	$167.95	$167.95	$168.00
Purchase #6	$34.47	10.707%	$38.1607	$38.16	$38.15	$38.20
Purchase #7	$131.39	6.315%	$139.6873	$139.69	$139.70	$139.70
7 purchase totals =	$674.88		$734.8526	$734.85	$734.80	$735.00