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	$228.87	13.576%	$259.9414	$259.94	$259.95	$259.90
Purchase #2	$138.88	13.125%	$157.108	$157.11	$157.10	$157.10
Purchase #3	$99.72	12.174%	$111.8599	$111.86	$111.85	$111.90
Purchase #4	$82.89	5.158%	$87.1655	$87.17	$87.15	$87.20
Purchase #5	$163.76	7.571%	$176.1583	$176.16	$176.15	$176.20
Purchase #6	$112.44	4.755%	$117.7865	$117.79	$117.80	$117.80
Purchase #7	$67.83	6.398%	$72.1698	$72.17	$72.15	$72.20
7 purchase totals =	$894.39		$982.1894	$982.20	$982.15	$982.30