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	$236.35	7.559%	$254.2157	$254.22	$254.20	$254.20
Purchase #2	$118.34	12.309%	$132.9065	$132.91	$132.90	$132.90
Purchase #3	$126.63	3.761%	$131.3926	$131.39	$131.40	$131.40
Purchase #4	$228.56	12.175%	$256.3872	$256.39	$256.40	$256.40
Purchase #5	$48.71	10.858%	$53.9989	$54.00	$54.00	$54.00
Purchase #6	$184.84	13.868%	$210.4736	$210.47	$210.45	$210.50
Purchase #7	$30.71	3.580%	$31.8094	$31.81	$31.80	$31.80
7 purchase totals =	$974.14		$1,071.1839	$1,071.19	$1,071.15	$1,071.20