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	$147.54	5.868%	$156.1976	$156.20	$156.20	$156.20
Purchase #2	$52.36	7.436%	$56.2535	$56.25	$56.25	$56.30
Purchase #3	$55.50	6.310%	$59.0021	$59.00	$59.00	$59.00
Purchase #4	$81.80	4.531%	$85.5064	$85.51	$85.50	$85.50
Purchase #5	$19.42	10.563%	$21.4713	$21.47	$21.45	$21.50
Purchase #6	$221.70	12.131%	$248.5944	$248.59	$248.60	$248.60
Purchase #7	$249.49	12.444%	$280.5365	$280.54	$280.55	$280.50
7 purchase totals =	$827.81		$907.5618	$907.56	$907.55	$907.60