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	$236.38	6.507%	$251.7612	$251.76	$251.75	$251.80
Purchase #2	$67.62	4.393%	$70.5905	$70.59	$70.60	$70.60
Purchase #3	$103.90	5.152%	$109.2529	$109.25	$109.25	$109.30
Purchase #4	$123.89	3.188%	$127.8396	$127.84	$127.85	$127.80
Purchase #5	$132.34	8.795%	$143.9793	$143.98	$144.00	$144.00
Purchase #6	$22.70	13.721%	$25.8147	$25.81	$25.80	$25.80
Purchase #7	$204.65	5.585%	$216.0797	$216.08	$216.10	$216.10
7 purchase totals =	$891.48		$945.3179	$945.31	$945.35	$945.40