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	$166.71	7.643%	$179.4516	$179.45	$179.45	$179.50
Purchase #2	$227.52	8.336%	$246.4861	$246.49	$246.50	$246.50
Purchase #3	$19.65	6.633%	$20.9534	$20.95	$20.95	$21.00
Purchase #4	$162.45	7.273%	$174.265	$174.27	$174.25	$174.30
Purchase #5	$172.81	7.366%	$185.5392	$185.54	$185.55	$185.50
Purchase #6	$187.43	8.472%	$203.3091	$203.31	$203.30	$203.30
Purchase #7	$9.36	12.339%	$10.5149	$10.51	$10.50	$10.50
7 purchase totals =	$945.93		$1,020.5193	$1,020.52	$1,020.50	$1,020.60