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	$249.42	4.507%	$260.6614	$260.66	$260.65	$260.70
Purchase #2	$75.78	3.189%	$78.1966	$78.20	$78.20	$78.20
Purchase #3	$36.75	8.341%	$39.8153	$39.82	$39.80	$39.80
Purchase #4	$67.29	4.749%	$70.4856	$70.49	$70.50	$70.50
Purchase #5	$117.96	12.303%	$132.4726	$132.47	$132.45	$132.50
Purchase #6	$156.78	11.291%	$174.482	$174.48	$174.50	$174.50
Purchase #7	$44.30	13.621%	$50.3341	$50.33	$50.35	$50.30
7 purchase totals =	$748.28		$806.4476	$806.45	$806.45	$806.50