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	$15.45	5.383%	$16.2817	$16.28	$16.30	$16.30
Purchase #2	$248.95	12.690%	$280.5418	$280.54	$280.55	$280.50
Purchase #3	$247.66	10.874%	$274.5905	$274.59	$274.60	$274.60
Purchase #4	$135.37	9.859%	$148.7161	$148.72	$148.70	$148.70
Purchase #5	$141.34	12.463%	$158.9552	$158.96	$158.95	$159.00
Purchase #6	$89.81	11.860%	$100.4615	$100.46	$100.45	$100.50
Purchase #7	$226.34	7.204%	$242.6455	$242.65	$242.65	$242.60
7 purchase totals =	$1,104.92		$1,222.1923	$1,222.20	$1,222.20	$1,222.20