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	$245.44	5.384%	$258.6545	$258.65	$258.65	$258.70
Purchase #2	$53.82	5.585%	$56.8258	$56.83	$56.85	$56.80
Purchase #3	$73.53	5.748%	$77.7565	$77.76	$77.75	$77.80
Purchase #4	$205.40	13.868%	$233.8849	$233.88	$233.90	$233.90
Purchase #5	$245.51	13.692%	$279.1252	$279.13	$279.15	$279.10
Purchase #6	$239.51	13.709%	$272.3444	$272.34	$272.35	$272.30
Purchase #7	$114.29	4.863%	$119.8479	$119.85	$119.85	$119.80
7 purchase totals =	$1,177.50		$1,298.4392	$1,298.44	$1,298.50	$1,298.40