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	$11.98	8.295%	$12.9737	$12.97	$12.95	$13.00
Purchase #2	$66.66	6.649%	$71.0922	$71.09	$71.10	$71.10
Purchase #3	$248.72	13.441%	$282.1505	$282.15	$282.15	$282.20
Purchase #4	$87.78	13.484%	$99.6163	$99.62	$99.60	$99.60
Purchase #5	$222.49	9.112%	$242.7633	$242.76	$242.75	$242.80
Purchase #6	$62.94	8.159%	$68.0753	$68.08	$68.10	$68.10
Purchase #7	$82.81	7.849%	$89.3098	$89.31	$89.30	$89.30
7 purchase totals =	$783.38		$865.9811	$865.98	$865.95	$866.10