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	$83.69	6.594%	$89.2085	$89.21	$89.20	$89.20
Purchase #2	$108.46	11.493%	$120.9253	$120.93	$120.95	$120.90
Purchase #3	$172.63	8.198%	$186.7822	$186.78	$186.80	$186.80
Purchase #4	$140.28	4.853%	$147.0878	$147.09	$147.10	$147.10
Purchase #5	$40.47	6.269%	$43.0071	$43.01	$43.00	$43.00
Purchase #6	$131.45	12.435%	$147.7958	$147.80	$147.80	$147.80
Purchase #7	$163.73	5.501%	$172.7368	$172.74	$172.75	$172.70
7 purchase totals =	$840.71		$907.5435	$907.56	$907.60	$907.50