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	$14.89	10.666%	$16.4782	$16.48	$16.50	$16.50
Purchase #2	$148.38	13.343%	$168.1783	$168.18	$168.20	$168.20
Purchase #3	$101.55	4.284%	$105.9004	$105.90	$105.90	$105.90
Purchase #4	$126.61	12.447%	$142.3691	$142.37	$142.35	$142.40
Purchase #5	$167.51	11.326%	$186.4822	$186.48	$186.50	$186.50
Purchase #6	$127.86	8.226%	$138.3778	$138.38	$138.40	$138.40
Purchase #7	$34.47	5.874%	$36.4948	$36.49	$36.50	$36.50
7 purchase totals =	$721.27		$794.2808	$794.28	$794.35	$794.40