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	$43.31	11.874%	$48.4526	$48.45	$48.45	$48.50
Purchase #2	$199.51	9.505%	$218.4734	$218.47	$218.45	$218.50
Purchase #3	$42.49	7.380%	$45.6258	$45.63	$45.65	$45.60
Purchase #4	$64.79	10.748%	$71.7536	$71.75	$71.75	$71.80
Purchase #5	$202.57	12.718%	$228.3329	$228.33	$228.35	$228.30
Purchase #6	$218.60	3.485%	$226.2182	$226.22	$226.20	$226.20
Purchase #7	$152.75	5.800%	$161.6095	$161.61	$161.60	$161.60
7 purchase totals =	$924.02		$1,000.4660	$1,000.46	$1,000.45	$1,000.50