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	$37.59	7.225%	$40.3059	$40.31	$40.30	$40.30
Purchase #2	$127.68	3.218%	$131.7887	$131.79	$131.80	$131.80
Purchase #3	$82.49	12.804%	$93.052	$93.05	$93.05	$93.10
Purchase #4	$242.39	4.825%	$254.0853	$254.09	$254.10	$254.10
Purchase #5	$144.75	6.270%	$153.8258	$153.83	$153.85	$153.80
Purchase #6	$86.98	8.584%	$94.4464	$94.45	$94.45	$94.40
Purchase #7	$28.83	9.665%	$31.6164	$31.62	$31.60	$31.60
7 purchase totals =	$750.71		$799.1205	$799.14	$799.15	$799.10