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	$159.69	4.222%	$166.4321	$166.43	$166.45	$166.40
Purchase #2	$216.35	7.142%	$231.8017	$231.80	$231.80	$231.80
Purchase #3	$55.90	6.605%	$59.5922	$59.59	$59.60	$59.60
Purchase #4	$68.59	6.291%	$72.905	$72.91	$72.90	$72.90
Purchase #5	$132.25	9.614%	$144.9645	$144.96	$144.95	$145.00
Purchase #6	$128.39	6.184%	$136.3296	$136.33	$136.35	$136.30
Purchase #7	$90.90	6.103%	$96.4476	$96.45	$96.45	$96.40
7 purchase totals =	$852.07		$908.4727	$908.47	$908.50	$908.40