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	$225.28	13.778%	$256.3191	$256.32	$256.30	$256.30
Purchase #2	$171.29	9.550%	$187.6482	$187.65	$187.65	$187.60
Purchase #3	$141.65	3.597%	$146.7452	$146.75	$146.75	$146.70
Purchase #4	$79.78	8.819%	$86.8158	$86.82	$86.80	$86.80
Purchase #5	$230.50	11.334%	$256.6249	$256.62	$256.60	$256.60
Purchase #6	$35.32	8.307%	$38.254	$38.25	$38.25	$38.30
Purchase #7	$53.59	5.617%	$56.6002	$56.60	$56.60	$56.60
7 purchase totals =	$937.41		$1,029.0074	$1,029.01	$1,028.95	$1,028.90