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	$16.82	9.113%	$18.3528	$18.35	$18.35	$18.40
Purchase #2	$208.42	9.114%	$227.4154	$227.42	$227.40	$227.40
Purchase #3	$163.73	13.805%	$186.3329	$186.33	$186.35	$186.30
Purchase #4	$59.83	3.618%	$61.9946	$61.99	$62.00	$62.00
Purchase #5	$181.68	4.705%	$190.228	$190.23	$190.25	$190.20
Purchase #6	$139.83	7.583%	$150.4333	$150.43	$150.45	$150.40
Purchase #7	$160.86	13.267%	$182.2013	$182.20	$182.20	$182.20
7 purchase totals =	$931.17		$1,016.9583	$1,016.95	$1,017.00	$1,016.90