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	$247.77	13.447%	$281.0876	$281.09	$281.10	$281.10
Purchase #2	$201.73	6.384%	$214.6084	$214.61	$214.60	$214.60
Purchase #3	$230.41	11.352%	$256.5661	$256.57	$256.55	$256.60
Purchase #4	$210.32	11.249%	$233.9789	$233.98	$234.00	$234.00
Purchase #5	$33.95	11.518%	$37.8604	$37.86	$37.85	$37.90
Purchase #6	$180.78	13.602%	$205.3697	$205.37	$205.35	$205.40
Purchase #7	$77.27	3.604%	$80.0548	$80.05	$80.05	$80.10
7 purchase totals =	$1,182.23		$1,309.5259	$1,309.53	$1,309.50	$1,309.70