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	$80.69	3.743%	$83.7102	$83.71	$83.70	$83.70
Purchase #2	$43.60	13.434%	$49.4572	$49.46	$49.45	$49.50
Purchase #3	$12.72	12.252%	$14.2785	$14.28	$14.30	$14.30
Purchase #4	$81.56	13.455%	$92.5339	$92.53	$92.55	$92.50
Purchase #5	$204.95	8.716%	$222.8134	$222.81	$222.80	$222.80
Purchase #6	$133.52	11.220%	$148.5009	$148.50	$148.50	$148.50
Purchase #7	$165.50	8.497%	$179.5625	$179.56	$179.55	$179.60
7 purchase totals =	$722.54		$790.8566	$790.85	$790.85	$790.90