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	$249.27	3.650%	$258.3684	$258.37	$258.35	$258.40
Purchase #2	$31.46	5.204%	$33.0972	$33.10	$33.10	$33.10
Purchase #3	$150.72	9.466%	$164.9872	$164.99	$165.00	$165.00
Purchase #4	$31.52	10.746%	$34.9071	$34.91	$34.90	$34.90
Purchase #5	$55.60	6.323%	$59.1156	$59.12	$59.10	$59.10
Purchase #6	$64.59	8.455%	$70.0511	$70.05	$70.05	$70.10
Purchase #7	$31.62	5.602%	$33.3914	$33.39	$33.40	$33.40
7 purchase totals =	$614.78		$653.9180	$653.93	$653.90	$654.00