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	$47.71	8.240%	$51.6413	$51.64	$51.65	$51.60
Purchase #2	$103.34	10.622%	$114.3168	$114.32	$114.30	$114.30
Purchase #3	$99.79	10.136%	$109.9047	$109.90	$109.90	$109.90
Purchase #4	$17.25	8.466%	$18.7104	$18.71	$18.70	$18.70
Purchase #5	$238.44	5.211%	$250.8651	$250.87	$250.85	$250.90
Purchase #6	$18.99	7.684%	$20.4492	$20.45	$20.45	$20.40
Purchase #7	$40.83	9.598%	$44.7489	$44.75	$44.75	$44.70
7 purchase totals =	$566.35		$610.6364	$610.64	$610.60	$610.50