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	$93.92	6.871%	$100.3732	$100.37	$100.35	$100.40
Purchase #2	$210.91	9.621%	$231.2017	$231.20	$231.20	$231.20
Purchase #3	$20.51	11.666%	$22.9027	$22.90	$22.90	$22.90
Purchase #4	$132.46	7.371%	$142.2236	$142.22	$142.20	$142.20
Purchase #5	$121.52	13.399%	$137.8025	$137.80	$137.80	$137.80
Purchase #6	$199.82	7.646%	$215.0982	$215.10	$215.10	$215.10
Purchase #7	$97.91	5.788%	$103.577	$103.58	$103.60	$103.60
7 purchase totals =	$877.05		$953.1789	$953.17	$953.15	$953.20