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	$50.71	3.656%	$52.564	$52.56	$52.55	$52.60
Purchase #2	$153.48	8.333%	$166.2695	$166.27	$166.25	$166.30
Purchase #3	$11.71	11.443%	$13.05	$13.05	$13.05	$13.10
Purchase #4	$146.58	13.129%	$165.8245	$165.82	$165.80	$165.80
Purchase #5	$94.38	4.479%	$98.6073	$98.61	$98.60	$98.60
Purchase #6	$148.40	12.540%	$167.0094	$167.01	$167.00	$167.00
Purchase #7	$140.77	7.324%	$151.08	$151.08	$151.10	$151.10
7 purchase totals =	$746.03		$814.4047	$814.40	$814.35	$814.50