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	$55.44	3.839%	$57.5683	$57.57	$57.55	$57.60
Purchase #2	$173.85	7.839%	$187.4781	$187.48	$187.50	$187.50
Purchase #3	$72.39	11.475%	$80.6968	$80.70	$80.70	$80.70
Purchase #4	$151.95	9.422%	$166.2667	$166.27	$166.25	$166.30
Purchase #5	$18.38	8.833%	$20.0035	$20.00	$20.00	$20.00
Purchase #6	$48.98	13.864%	$55.7706	$55.77	$55.75	$55.80
Purchase #7	$58.43	5.450%	$61.6144	$61.61	$61.60	$61.60
7 purchase totals =	$579.42		$629.3984	$629.40	$629.35	$629.50