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	$160.62	4.773%	$168.2864	$168.29	$168.30	$168.30
Purchase #2	$79.75	11.805%	$89.1645	$89.16	$89.15	$89.20
Purchase #3	$105.53	11.696%	$117.8728	$117.87	$117.85	$117.90
Purchase #4	$145.98	5.435%	$153.914	$153.91	$153.90	$153.90
Purchase #5	$16.75	9.488%	$18.3392	$18.34	$18.35	$18.30
Purchase #6	$109.55	13.169%	$123.9766	$123.98	$124.00	$124.00
Purchase #7	$24.45	3.716%	$25.3586	$25.36	$25.35	$25.40
7 purchase totals =	$642.63		$696.9121	$696.91	$696.90	$697.00