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	$161.73	3.150%	$166.8245	$166.82	$166.80	$166.80
Purchase #2	$100.72	5.121%	$105.8779	$105.88	$105.90	$105.90
Purchase #3	$122.85	13.151%	$139.006	$139.01	$139.00	$139.00
Purchase #4	$120.29	7.870%	$129.7568	$129.76	$129.75	$129.80
Purchase #5	$146.68	12.442%	$164.9299	$164.93	$164.95	$164.90
Purchase #6	$22.83	6.272%	$24.2619	$24.26	$24.25	$24.30
Purchase #7	$102.37	10.210%	$112.822	$112.82	$112.80	$112.80
7 purchase totals =	$777.47		$843.4790	$843.48	$843.45	$843.50