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	$41.65	4.373%	$43.4714	$43.47	$43.45	$43.50
Purchase #2	$144.71	9.262%	$158.113	$158.11	$158.10	$158.10
Purchase #3	$42.89	3.312%	$44.3105	$44.31	$44.30	$44.30
Purchase #4	$189.46	5.727%	$200.3104	$200.31	$200.30	$200.30
Purchase #5	$103.29	9.747%	$113.3577	$113.36	$113.35	$113.40
Purchase #6	$20.78	5.230%	$21.8668	$21.87	$21.85	$21.90
Purchase #7	$19.83	5.687%	$20.9577	$20.96	$20.95	$21.00
7 purchase totals =	$562.61		$602.3875	$602.39	$602.30	$602.50