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	$249.39	12.618%	$280.858	$280.86	$280.85	$280.90
Purchase #2	$28.93	13.707%	$32.8954	$32.90	$32.90	$32.90
Purchase #3	$162.25	8.666%	$176.3106	$176.31	$176.30	$176.30
Purchase #4	$103.99	7.589%	$111.8818	$111.88	$111.90	$111.90
Purchase #5	$233.79	3.468%	$241.8978	$241.90	$241.90	$241.90
Purchase #6	$230.66	9.427%	$252.4043	$252.40	$252.40	$252.40
Purchase #7	$215.98	4.187%	$225.0231	$225.02	$225.00	$225.00
7 purchase totals =	$1,224.99		$1,321.2710	$1,321.27	$1,321.25	$1,321.30