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	$90.96	9.301%	$99.4202	$99.42	$99.40	$99.40
Purchase #2	$78.53	4.389%	$81.9767	$81.98	$82.00	$82.00
Purchase #3	$155.45	13.389%	$176.2632	$176.26	$176.25	$176.30
Purchase #4	$33.71	12.206%	$37.8246	$37.82	$37.80	$37.80
Purchase #5	$157.37	8.178%	$170.2397	$170.24	$170.25	$170.20
Purchase #6	$24.37	13.348%	$27.6229	$27.62	$27.60	$27.60
Purchase #7	$237.54	12.309%	$266.7788	$266.78	$266.80	$266.80
7 purchase totals =	$777.93		$860.1261	$860.12	$860.10	$860.10