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	$31.52	9.733%	$34.5878	$34.59	$34.60	$34.60
Purchase #2	$136.86	11.782%	$152.9848	$152.98	$153.00	$153.00
Purchase #3	$231.91	7.745%	$249.8714	$249.87	$249.85	$249.90
Purchase #4	$98.30	13.556%	$111.6255	$111.63	$111.65	$111.60
Purchase #5	$113.54	6.786%	$121.2448	$121.24	$121.25	$121.20
Purchase #6	$128.61	11.808%	$143.7963	$143.80	$143.80	$143.80
Purchase #7	$39.83	13.857%	$45.3492	$45.35	$45.35	$45.30
7 purchase totals =	$780.57		$859.4598	$859.46	$859.50	$859.40