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	$18.54	9.398%	$20.2824	$20.28	$20.30	$20.30
Purchase #2	$169.61	3.688%	$175.8652	$175.87	$175.85	$175.90
Purchase #3	$191.34	4.240%	$199.4528	$199.45	$199.45	$199.50
Purchase #4	$86.72	4.155%	$90.3232	$90.32	$90.30	$90.30
Purchase #5	$94.80	6.229%	$100.7051	$100.71	$100.70	$100.70
Purchase #6	$40.67	7.436%	$43.6942	$43.69	$43.70	$43.70
Purchase #7	$6.28	9.366%	$6.8682	$6.87	$6.85	$6.90
7 purchase totals =	$607.96		$637.1911	$637.19	$637.15	$637.30