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	$92.42	7.633%	$99.4744	$99.47	$99.45	$99.50
Purchase #2	$129.28	11.326%	$143.9223	$143.92	$143.90	$143.90
Purchase #3	$173.35	7.788%	$186.8505	$186.85	$186.85	$186.90
Purchase #4	$11.78	12.545%	$13.2578	$13.26	$13.25	$13.30
Purchase #5	$140.66	9.350%	$153.8117	$153.81	$153.80	$153.80
Purchase #6	$52.53	6.311%	$55.8452	$55.85	$55.85	$55.80
Purchase #7	$145.26	11.704%	$162.2612	$162.26	$162.25	$162.30
7 purchase totals =	$745.28		$815.4231	$815.42	$815.35	$815.50