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	$199.34	6.141%	$211.5815	$211.58	$211.60	$211.60
Purchase #2	$129.64	3.828%	$134.6026	$134.60	$134.60	$134.60
Purchase #3	$99.74	6.125%	$105.8491	$105.85	$105.85	$105.80
Purchase #4	$83.62	7.695%	$90.0546	$90.05	$90.05	$90.10
Purchase #5	$19.60	4.418%	$20.4659	$20.47	$20.45	$20.50
Purchase #6	$35.47	11.603%	$39.5856	$39.59	$39.60	$39.60
Purchase #7	$249.69	8.702%	$271.418	$271.42	$271.40	$271.40
7 purchase totals =	$817.10		$873.5573	$873.56	$873.55	$873.60