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	$249.57	10.523%	$275.8323	$275.83	$275.85	$275.80
Purchase #2	$66.85	5.603%	$70.5956	$70.60	$70.60	$70.60
Purchase #3	$112.88	13.460%	$128.0736	$128.07	$128.05	$128.10
Purchase #4	$39.89	8.730%	$43.3724	$43.37	$43.35	$43.40
Purchase #5	$153.72	6.740%	$164.0807	$164.08	$164.10	$164.10
Purchase #6	$242.67	9.710%	$266.2333	$266.23	$266.25	$266.20
Purchase #7	$242.62	12.737%	$273.5225	$273.52	$273.50	$273.50
7 purchase totals =	$1,108.20		$1,221.7104	$1,221.70	$1,221.70	$1,221.70