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	$57.38	4.207%	$59.794	$59.79	$59.80	$59.80
Purchase #2	$66.72	6.450%	$71.0234	$71.02	$71.00	$71.00
Purchase #3	$122.79	11.314%	$136.6825	$136.68	$136.70	$136.70
Purchase #4	$71.71	3.848%	$74.4694	$74.47	$74.45	$74.50
Purchase #5	$74.31	10.260%	$81.9342	$81.93	$81.95	$81.90
Purchase #6	$55.77	6.740%	$59.5289	$59.53	$59.55	$59.50
Purchase #7	$79.56	8.857%	$86.6066	$86.61	$86.60	$86.60
7 purchase totals =	$528.24		$570.0390	$570.03	$570.05	$570.00