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	$36.35	10.517%	$40.1729	$40.17	$40.15	$40.20
Purchase #2	$37.38	5.141%	$39.3017	$39.30	$39.30	$39.30
Purchase #3	$166.44	11.314%	$185.271	$185.27	$185.25	$185.30
Purchase #4	$125.40	12.288%	$140.8092	$140.81	$140.80	$140.80
Purchase #5	$90.51	5.137%	$95.1595	$95.16	$95.15	$95.20
Purchase #6	$13.47	4.224%	$14.039	$14.04	$14.05	$14.00
Purchase #7	$161.27	4.542%	$168.5949	$168.59	$168.60	$168.60
7 purchase totals =	$630.82		$683.3482	$683.34	$683.30	$683.40