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	$123.57	12.382%	$138.8704	$138.87	$138.85	$138.90
Purchase #2	$13.72	13.272%	$15.5409	$15.54	$15.55	$15.50
Purchase #3	$142.95	13.411%	$162.121	$162.12	$162.10	$162.10
Purchase #4	$79.69	13.485%	$90.4362	$90.44	$90.45	$90.40
Purchase #5	$250.29	4.821%	$262.3565	$262.36	$262.35	$262.40
Purchase #6	$215.52	13.336%	$244.2617	$244.26	$244.25	$244.30
Purchase #7	$107.83	4.333%	$112.5023	$112.50	$112.50	$112.50
7 purchase totals =	$933.57		$1,026.0890	$1,026.09	$1,026.05	$1,026.10