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	$71.45	11.719%	$79.8232	$79.82	$79.80	$79.80
Purchase #2	$48.42	3.197%	$49.968	$49.97	$49.95	$50.00
Purchase #3	$61.61	6.386%	$65.5444	$65.54	$65.55	$65.50
Purchase #4	$109.38	8.674%	$118.8676	$118.87	$118.85	$118.90
Purchase #5	$159.82	11.867%	$178.7858	$178.79	$178.80	$178.80
Purchase #6	$50.93	7.725%	$54.8643	$54.86	$54.85	$54.90
Purchase #7	$72.52	12.141%	$81.3247	$81.32	$81.30	$81.30
7 purchase totals =	$574.13		$629.1780	$629.17	$629.10	$629.20