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	$230.37	5.678%	$243.4504	$243.45	$243.45	$243.50
Purchase #2	$118.69	11.364%	$132.1779	$132.18	$132.20	$132.20
Purchase #3	$100.66	6.812%	$107.517	$107.52	$107.50	$107.50
Purchase #4	$81.57	11.231%	$90.7311	$90.73	$90.75	$90.70
Purchase #5	$19.98	6.137%	$21.2062	$21.21	$21.20	$21.20
Purchase #6	$105.82	3.385%	$109.402	$109.40	$109.40	$109.40
Purchase #7	$132.79	5.196%	$139.6898	$139.69	$139.70	$139.70
7 purchase totals =	$789.88		$844.1744	$844.18	$844.20	$844.20