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	$172.43	9.131%	$188.1746	$188.17	$188.15	$188.20
Purchase #2	$140.47	8.522%	$152.4409	$152.44	$152.45	$152.40
Purchase #3	$187.78	13.713%	$213.5303	$213.53	$213.55	$213.50
Purchase #4	$214.54	7.792%	$231.257	$231.26	$231.25	$231.30
Purchase #5	$116.55	13.442%	$132.2167	$132.22	$132.20	$132.20
Purchase #6	$74.97	9.602%	$82.1686	$82.17	$82.15	$82.20
Purchase #7	$71.59	10.429%	$79.0561	$79.06	$79.05	$79.10
7 purchase totals =	$978.33		$1,078.8442	$1,078.85	$1,078.80	$1,078.90