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	$43.93	13.713%	$49.9541	$49.95	$49.95	$50.00
Purchase #2	$62.96	11.804%	$70.3918	$70.39	$70.40	$70.40
Purchase #3	$18.90	8.495%	$20.5056	$20.51	$20.50	$20.50
Purchase #4	$145.88	5.728%	$154.236	$154.24	$154.25	$154.20
Purchase #5	$88.89	11.844%	$99.4181	$99.42	$99.40	$99.40
Purchase #6	$141.72	3.214%	$146.2749	$146.27	$146.25	$146.30
Purchase #7	$46.95	8.420%	$50.9032	$50.90	$50.90	$50.90
7 purchase totals =	$549.23		$591.6837	$591.68	$591.65	$591.70