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	$12.30	9.748%	$13.499	$13.50	$13.50	$13.50
Purchase #2	$138.90	7.159%	$148.8439	$148.84	$148.85	$148.80
Purchase #3	$43.30	10.584%	$47.8829	$47.88	$47.90	$47.90
Purchase #4	$103.29	3.715%	$107.1272	$107.13	$107.15	$107.10
Purchase #5	$38.72	4.125%	$40.3172	$40.32	$40.30	$40.30
Purchase #6	$31.28	3.468%	$32.3648	$32.36	$32.35	$32.40
Purchase #7	$179.47	13.586%	$203.8528	$203.85	$203.85	$203.90
7 purchase totals =	$547.26		$593.8878	$593.88	$593.90	$593.90