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	$24.94	6.242%	$26.4968	$26.50	$26.50	$26.50
Purchase #2	$46.94	7.544%	$50.4812	$50.48	$50.50	$50.50
Purchase #3	$242.45	11.422%	$270.1426	$270.14	$270.15	$270.10
Purchase #4	$161.77	10.615%	$178.9419	$178.94	$178.95	$178.90
Purchase #5	$78.85	13.153%	$89.2211	$89.22	$89.20	$89.20
Purchase #6	$182.77	4.640%	$191.2505	$191.25	$191.25	$191.30
Purchase #7	$88.59	12.181%	$99.3811	$99.38	$99.40	$99.40
7 purchase totals =	$826.31		$905.9152	$905.91	$905.95	$905.90