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	$19.93	8.362%	$21.5965	$21.60	$21.60	$21.60
Purchase #2	$71.69	11.685%	$80.067	$80.07	$80.05	$80.10
Purchase #3	$104.78	7.494%	$112.6322	$112.63	$112.65	$112.60
Purchase #4	$198.83	10.364%	$219.4367	$219.44	$219.45	$219.40
Purchase #5	$137.39	9.612%	$150.5959	$150.60	$150.60	$150.60
Purchase #6	$241.86	3.252%	$249.7253	$249.73	$249.75	$249.70
Purchase #7	$159.40	10.681%	$176.4255	$176.43	$176.45	$176.40
7 purchase totals =	$933.88		$1,010.4791	$1,010.50	$1,010.55	$1,010.40