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	$171.72	4.309%	$179.1194	$179.12	$179.10	$179.10
Purchase #2	$218.88	5.762%	$231.4919	$231.49	$231.50	$231.50
Purchase #3	$121.37	12.393%	$136.4114	$136.41	$136.40	$136.40
Purchase #4	$58.78	9.579%	$64.4105	$64.41	$64.40	$64.40
Purchase #5	$56.37	12.204%	$63.2494	$63.25	$63.25	$63.20
Purchase #6	$38.81	12.183%	$43.5382	$43.54	$43.55	$43.50
Purchase #7	$172.48	10.421%	$190.4541	$190.45	$190.45	$190.50
7 purchase totals =	$838.41		$908.6749	$908.67	$908.65	$908.60