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	$126.51	8.357%	$137.0824	$137.08	$137.10	$137.10
Purchase #2	$45.60	10.631%	$50.4477	$50.45	$50.45	$50.40
Purchase #3	$134.68	5.704%	$142.3621	$142.36	$142.35	$142.40
Purchase #4	$78.61	8.746%	$85.4852	$85.49	$85.50	$85.50
Purchase #5	$25.85	6.329%	$27.486	$27.49	$27.50	$27.50
Purchase #6	$69.38	3.306%	$71.6737	$71.67	$71.65	$71.70
Purchase #7	$86.35	11.103%	$95.9374	$95.94	$95.95	$95.90
7 purchase totals =	$566.98		$610.4745	$610.48	$610.50	$610.50