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	$10.99	13.597%	$12.4843	$12.48	$12.50	$12.50
Purchase #2	$98.70	12.645%	$111.1806	$111.18	$111.20	$111.20
Purchase #3	$65.88	5.733%	$69.6569	$69.66	$69.65	$69.70
Purchase #4	$46.28	10.775%	$51.2667	$51.27	$51.25	$51.30
Purchase #5	$37.58	13.146%	$42.5203	$42.52	$42.50	$42.50
Purchase #6	$51.85	7.632%	$55.8072	$55.81	$55.80	$55.80
Purchase #7	$106.30	8.510%	$115.3461	$115.35	$115.35	$115.30
7 purchase totals =	$417.58		$458.2621	$458.27	$458.25	$458.30