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	$123.27	5.737%	$130.342	$130.34	$130.35	$130.30
Purchase #2	$66.79	8.623%	$72.5493	$72.55	$72.55	$72.50
Purchase #3	$57.65	8.499%	$62.5497	$62.55	$62.55	$62.50
Purchase #4	$110.54	5.794%	$116.9447	$116.94	$116.95	$116.90
Purchase #5	$197.40	6.706%	$210.6376	$210.64	$210.65	$210.60
Purchase #6	$249.93	12.348%	$280.7914	$280.79	$280.80	$280.80
Purchase #7	$37.25	4.653%	$38.9832	$38.98	$39.00	$39.00
7 purchase totals =	$842.83		$912.7979	$912.79	$912.85	$912.60