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	$15.34	12.556%	$17.2661	$17.27	$17.25	$17.30
Purchase #2	$246.87	13.561%	$280.348	$280.35	$280.35	$280.30
Purchase #3	$175.43	13.788%	$199.6183	$199.62	$199.60	$199.60
Purchase #4	$118.49	4.265%	$123.5436	$123.54	$123.55	$123.50
Purchase #5	$71.74	4.121%	$74.6964	$74.70	$74.70	$74.70
Purchase #6	$83.93	7.257%	$90.0208	$90.02	$90.00	$90.00
Purchase #7	$158.46	13.502%	$179.8553	$179.86	$179.85	$179.90
7 purchase totals =	$870.26		$965.3485	$965.36	$965.30	$965.30