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	$35.25	13.425%	$39.9823	$39.98	$40.00	$40.00
Purchase #2	$212.42	13.196%	$240.4509	$240.45	$240.45	$240.50
Purchase #3	$217.73	9.605%	$238.643	$238.64	$238.65	$238.60
Purchase #4	$56.55	4.786%	$59.2565	$59.26	$59.25	$59.30
Purchase #5	$216.91	8.172%	$234.6359	$234.64	$234.65	$234.60
Purchase #6	$174.66	5.691%	$184.5999	$184.60	$184.60	$184.60
Purchase #7	$86.51	10.376%	$95.4863	$95.49	$95.50	$95.50
7 purchase totals =	$1,000.03		$1,093.0548	$1,093.06	$1,093.10	$1,093.10