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	$40.76	4.512%	$42.5991	$42.60	$42.60	$42.60
Purchase #2	$69.37	4.812%	$72.7081	$72.71	$72.70	$72.70
Purchase #3	$81.34	7.513%	$87.4511	$87.45	$87.45	$87.50
Purchase #4	$226.80	9.521%	$248.3936	$248.39	$248.40	$248.40
Purchase #5	$38.40	13.693%	$43.6581	$43.66	$43.65	$43.70
Purchase #6	$89.83	6.700%	$95.8486	$95.85	$95.85	$95.80
Purchase #7	$110.68	6.785%	$118.1896	$118.19	$118.20	$118.20
7 purchase totals =	$657.18		$708.8482	$708.85	$708.85	$708.90