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	$51.40	9.470%	$56.2676	$56.27	$56.25	$56.30
Purchase #2	$102.46	3.809%	$106.3627	$106.36	$106.35	$106.40
Purchase #3	$138.59	10.670%	$153.3776	$153.38	$153.40	$153.40
Purchase #4	$67.90	13.661%	$77.1758	$77.18	$77.20	$77.20
Purchase #5	$249.59	12.301%	$280.2921	$280.29	$280.30	$280.30
Purchase #6	$141.60	6.514%	$150.8238	$150.82	$150.80	$150.80
Purchase #7	$114.40	4.179%	$119.1808	$119.18	$119.20	$119.20
7 purchase totals =	$865.94		$943.4804	$943.48	$943.50	$943.60