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	$185.30	3.385%	$191.5724	$191.57	$191.55	$191.60
Purchase #2	$166.45	12.572%	$187.3761	$187.38	$187.40	$187.40
Purchase #3	$95.43	12.603%	$107.457	$107.46	$107.45	$107.50
Purchase #4	$155.58	4.532%	$162.6309	$162.63	$162.65	$162.60
Purchase #5	$41.62	9.408%	$45.5356	$45.54	$45.55	$45.50
Purchase #6	$139.32	3.284%	$143.8953	$143.90	$143.90	$143.90
Purchase #7	$115.82	8.857%	$126.0782	$126.08	$126.10	$126.10
7 purchase totals =	$899.52		$964.5455	$964.56	$964.60	$964.60