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	$159.82	3.600%	$165.5735	$165.57	$165.55	$165.60
Purchase #2	$67.46	10.227%	$74.3591	$74.36	$74.35	$74.40
Purchase #3	$162.92	11.459%	$181.589	$181.59	$181.60	$181.60
Purchase #4	$72.54	5.131%	$76.262	$76.26	$76.25	$76.30
Purchase #5	$103.32	12.766%	$116.5098	$116.51	$116.50	$116.50
Purchase #6	$95.63	5.366%	$100.7615	$100.76	$100.75	$100.80
Purchase #7	$81.84	10.612%	$90.5249	$90.52	$90.50	$90.50
7 purchase totals =	$743.53		$805.5798	$805.57	$805.50	$805.70