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	$46.85	7.801%	$50.5048	$50.50	$50.50	$50.50
Purchase #2	$100.98	10.254%	$111.3345	$111.33	$111.35	$111.30
Purchase #3	$90.55	12.643%	$101.9982	$102.00	$102.00	$102.00
Purchase #4	$16.80	6.493%	$17.8908	$17.89	$17.90	$17.90
Purchase #5	$57.75	13.604%	$65.6063	$65.61	$65.60	$65.60
Purchase #6	$8.32	6.419%	$8.8541	$8.85	$8.85	$8.90
Purchase #7	$93.89	5.737%	$99.2765	$99.28	$99.30	$99.30
7 purchase totals =	$415.14		$455.4652	$455.46	$455.50	$455.50