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	$139.80	6.481%	$148.8604	$148.86	$148.85	$148.90
Purchase #2	$78.57	10.215%	$86.5959	$86.60	$86.60	$86.60
Purchase #3	$27.90	5.195%	$29.3494	$29.35	$29.35	$29.30
Purchase #4	$13.52	10.761%	$14.9749	$14.97	$14.95	$15.00
Purchase #5	$132.88	13.222%	$150.4494	$150.45	$150.45	$150.40
Purchase #6	$49.63	13.777%	$56.4675	$56.47	$56.45	$56.50
Purchase #7	$233.51	13.243%	$264.4337	$264.43	$264.45	$264.40
7 purchase totals =	$675.81		$751.1312	$751.13	$751.10	$751.10