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	$46.51	9.718%	$51.0298	$51.03	$51.05	$51.00
Purchase #2	$174.79	7.182%	$187.3434	$187.34	$187.35	$187.30
Purchase #3	$53.89	7.653%	$58.0142	$58.01	$58.00	$58.00
Purchase #4	$233.49	13.269%	$264.4718	$264.47	$264.45	$264.50
Purchase #5	$59.89	13.634%	$68.0554	$68.06	$68.05	$68.10
Purchase #6	$34.93	11.456%	$38.9316	$38.93	$38.95	$38.90
Purchase #7	$59.93	12.307%	$67.3056	$67.31	$67.30	$67.30
7 purchase totals =	$663.43		$735.1518	$735.15	$735.15	$735.10