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	$61.65	7.633%	$66.3557	$66.36	$66.35	$66.40
Purchase #2	$140.62	10.673%	$155.6284	$155.63	$155.65	$155.60
Purchase #3	$230.86	7.793%	$248.8509	$248.85	$248.85	$248.90
Purchase #4	$70.38	12.859%	$79.4302	$79.43	$79.45	$79.40
Purchase #5	$108.35	3.181%	$111.7966	$111.80	$111.80	$111.80
Purchase #6	$122.83	6.260%	$130.5192	$130.52	$130.50	$130.50
Purchase #7	$40.96	3.598%	$42.4337	$42.43	$42.45	$42.40
7 purchase totals =	$775.65		$835.0147	$835.02	$835.05	$835.00