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	$129.43	3.160%	$133.52	$133.52	$133.50	$133.50
Purchase #2	$110.43	4.624%	$115.5363	$115.54	$115.55	$115.50
Purchase #3	$87.48	3.326%	$90.3896	$90.39	$90.40	$90.40
Purchase #4	$225.85	13.187%	$255.6328	$255.63	$255.65	$255.60
Purchase #5	$201.30	12.826%	$227.1187	$227.12	$227.10	$227.10
Purchase #6	$12.48	6.719%	$13.3185	$13.32	$13.30	$13.30
Purchase #7	$57.30	13.407%	$64.9822	$64.98	$65.00	$65.00
7 purchase totals =	$824.27		$900.4981	$900.50	$900.50	$900.40