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	$177.72	6.661%	$189.5579	$189.56	$189.55	$189.60
Purchase #2	$225.73	8.641%	$245.2353	$245.24	$245.25	$245.20
Purchase #3	$21.51	9.493%	$23.5519	$23.55	$23.55	$23.60
Purchase #4	$38.48	9.725%	$42.2222	$42.22	$42.20	$42.20
Purchase #5	$133.54	7.726%	$143.8573	$143.86	$143.85	$143.90
Purchase #6	$127.29	7.519%	$136.8609	$136.86	$136.85	$136.90
Purchase #7	$207.25	11.290%	$230.6485	$230.65	$230.65	$230.60
7 purchase totals =	$931.52		$1,011.9340	$1,011.94	$1,011.90	$1,012.00