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	$52.76	3.456%	$54.5834	$54.58	$54.60	$54.60
Purchase #2	$57.73	4.685%	$60.4347	$60.43	$60.45	$60.40
Purchase #3	$246.49	13.533%	$279.8475	$279.85	$279.85	$279.80
Purchase #4	$163.30	8.141%	$176.5943	$176.59	$176.60	$176.60
Purchase #5	$51.71	11.844%	$57.8345	$57.83	$57.85	$57.80
Purchase #6	$29.35	6.443%	$31.241	$31.24	$31.25	$31.20
Purchase #7	$85.31	13.363%	$96.71	$96.71	$96.70	$96.70
7 purchase totals =	$686.65		$757.2454	$757.23	$757.30	$757.10