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	$162.27	3.847%	$168.5125	$168.51	$168.50	$168.50
Purchase #2	$29.30	7.468%	$31.4881	$31.49	$31.50	$31.50
Purchase #3	$8.42	5.411%	$8.8756	$8.88	$8.90	$8.90
Purchase #4	$153.43	9.454%	$167.9353	$167.94	$167.95	$167.90
Purchase #5	$17.95	7.458%	$19.2887	$19.29	$19.30	$19.30
Purchase #6	$126.45	5.384%	$133.2581	$133.26	$133.25	$133.30
Purchase #7	$83.69	8.503%	$90.8062	$90.81	$90.80	$90.80
7 purchase totals =	$581.51		$620.1645	$620.18	$620.20	$620.20