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	$208.95	6.163%	$221.8276	$221.83	$221.85	$221.80
Purchase #2	$98.86	12.862%	$111.5754	$111.58	$111.60	$111.60
Purchase #3	$107.50	12.228%	$120.6451	$120.65	$120.65	$120.60
Purchase #4	$75.36	4.189%	$78.5168	$78.52	$78.50	$78.50
Purchase #5	$55.51	10.717%	$61.459	$61.46	$61.45	$61.50
Purchase #6	$30.74	7.758%	$33.1248	$33.12	$33.10	$33.10
Purchase #7	$57.55	7.569%	$61.906	$61.91	$61.90	$61.90
7 purchase totals =	$634.47		$689.0547	$689.07	$689.05	$689.00