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	$22.30	3.418%	$23.0622	$23.06	$23.05	$23.10
Purchase #2	$19.37	5.398%	$20.4156	$20.42	$20.40	$20.40
Purchase #3	$153.79	12.337%	$172.7631	$172.76	$172.75	$172.80
Purchase #4	$124.90	7.216%	$133.9128	$133.91	$133.90	$133.90
Purchase #5	$104.35	5.395%	$109.9797	$109.98	$110.00	$110.00
Purchase #6	$143.32	10.697%	$158.6509	$158.65	$158.65	$158.70
Purchase #7	$43.65	11.440%	$48.6436	$48.64	$48.65	$48.60
7 purchase totals =	$611.68		$667.4279	$667.42	$667.40	$667.50