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	$200.37	5.226%	$210.8413	$210.84	$210.85	$210.80
Purchase #2	$124.67	10.363%	$137.5896	$137.59	$137.60	$137.60
Purchase #3	$189.92	12.584%	$213.8195	$213.82	$213.80	$213.80
Purchase #4	$34.69	12.867%	$39.1536	$39.15	$39.15	$39.20
Purchase #5	$33.82	13.718%	$38.4594	$38.46	$38.45	$38.50
Purchase #6	$182.78	9.548%	$200.2318	$200.23	$200.25	$200.20
Purchase #7	$81.49	12.562%	$91.7268	$91.73	$91.75	$91.70
7 purchase totals =	$847.74		$931.8220	$931.82	$931.85	$931.80