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	$33.43	9.277%	$36.5313	$36.53	$36.55	$36.50
Purchase #2	$178.86	11.129%	$198.7653	$198.77	$198.75	$198.80
Purchase #3	$213.71	9.300%	$233.585	$233.59	$233.60	$233.60
Purchase #4	$90.56	10.813%	$100.3523	$100.35	$100.35	$100.40
Purchase #5	$101.97	3.234%	$105.2677	$105.27	$105.25	$105.30
Purchase #6	$160.78	9.504%	$176.0605	$176.06	$176.05	$176.10
Purchase #7	$93.85	3.134%	$96.7913	$96.79	$96.80	$96.80
7 purchase totals =	$873.16		$947.3534	$947.36	$947.35	$947.50