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	$46.32	12.141%	$51.9437	$51.94	$51.95	$51.90
Purchase #2	$32.48	8.413%	$35.2125	$35.21	$35.20	$35.20
Purchase #3	$103.89	5.548%	$109.6538	$109.65	$109.65	$109.70
Purchase #4	$73.53	6.826%	$78.5492	$78.55	$78.55	$78.50
Purchase #5	$51.61	8.816%	$56.1599	$56.16	$56.15	$56.20
Purchase #6	$111.97	10.332%	$123.5387	$123.54	$123.55	$123.50
Purchase #7	$48.65	13.189%	$55.0664	$55.07	$55.05	$55.10
7 purchase totals =	$468.45		$510.1242	$510.12	$510.10	$510.10