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	$66.94	6.293%	$71.1525	$71.15	$71.15	$71.20
Purchase #2	$104.30	5.160%	$109.6819	$109.68	$109.70	$109.70
Purchase #3	$166.72	5.250%	$175.4728	$175.47	$175.45	$175.50
Purchase #4	$243.76	3.730%	$252.8522	$252.85	$252.85	$252.90
Purchase #5	$69.31	10.588%	$76.6485	$76.65	$76.65	$76.60
Purchase #6	$83.49	7.316%	$89.5981	$89.60	$89.60	$89.60
Purchase #7	$38.95	4.295%	$40.6229	$40.62	$40.60	$40.60
7 purchase totals =	$773.47		$816.0289	$816.02	$816.00	$816.10