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	$160.55	12.796%	$181.094	$181.09	$181.10	$181.10
Purchase #2	$122.78	3.754%	$127.3892	$127.39	$127.40	$127.40
Purchase #3	$175.79	4.398%	$183.5212	$183.52	$183.50	$183.50
Purchase #4	$46.27	13.452%	$52.4942	$52.49	$52.50	$52.50
Purchase #5	$208.82	6.394%	$222.172	$222.17	$222.15	$222.20
Purchase #6	$108.35	8.410%	$117.4622	$117.46	$117.45	$117.50
Purchase #7	$128.35	8.453%	$139.1994	$139.20	$139.20	$139.20
7 purchase totals =	$950.91		$1,023.3322	$1,023.32	$1,023.30	$1,023.40