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	$35.47	11.638%	$39.598	$39.60	$39.60	$39.60
Purchase #2	$94.59	5.296%	$99.5995	$99.60	$99.60	$99.60
Purchase #3	$205.29	9.816%	$225.4413	$225.44	$225.45	$225.40
Purchase #4	$153.70	7.377%	$165.0384	$165.04	$165.05	$165.00
Purchase #5	$83.72	4.796%	$87.7352	$87.74	$87.75	$87.70
Purchase #6	$50.69	7.220%	$54.3498	$54.35	$54.35	$54.30
Purchase #7	$122.48	13.536%	$139.0589	$139.06	$139.05	$139.10
7 purchase totals =	$745.94		$810.8211	$810.83	$810.85	$810.70