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	$79.26	4.262%	$82.6381	$82.64	$82.65	$82.60
Purchase #2	$82.55	8.515%	$89.5791	$89.58	$89.60	$89.60
Purchase #3	$127.95	6.324%	$136.0416	$136.04	$136.05	$136.00
Purchase #4	$50.90	6.229%	$54.0706	$54.07	$54.05	$54.10
Purchase #5	$226.37	13.745%	$257.4846	$257.48	$257.50	$257.50
Purchase #6	$178.75	12.375%	$200.8703	$200.87	$200.85	$200.90
Purchase #7	$44.99	9.599%	$49.3086	$49.31	$49.30	$49.30
7 purchase totals =	$790.77		$869.9929	$869.99	$870.00	$870.00