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	$119.70	7.163%	$128.2741	$128.27	$128.25	$128.30
Purchase #2	$128.78	4.332%	$134.3587	$134.36	$134.35	$134.40
Purchase #3	$172.48	4.712%	$180.6073	$180.61	$180.60	$180.60
Purchase #4	$123.69	6.612%	$131.8684	$131.87	$131.85	$131.90
Purchase #5	$65.73	10.335%	$72.5232	$72.52	$72.50	$72.50
Purchase #6	$42.76	9.670%	$46.8949	$46.89	$46.90	$46.90
Purchase #7	$184.46	8.500%	$200.1391	$200.14	$200.15	$200.10
7 purchase totals =	$837.60		$894.6657	$894.66	$894.60	$894.70