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	$42.50	13.626%	$48.2911	$48.29	$48.30	$48.30
Purchase #2	$124.56	10.151%	$137.2041	$137.20	$137.20	$137.20
Purchase #3	$31.79	5.693%	$33.5998	$33.60	$33.60	$33.60
Purchase #4	$20.76	12.707%	$23.398	$23.40	$23.40	$23.40
Purchase #5	$137.49	13.858%	$156.5434	$156.54	$156.55	$156.50
Purchase #6	$122.29	9.458%	$133.8562	$133.86	$133.85	$133.90
Purchase #7	$62.69	4.594%	$65.57	$65.57	$65.55	$65.60
7 purchase totals =	$542.08		$598.4626	$598.46	$598.45	$598.50