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	$179.35	4.545%	$187.5015	$187.50	$187.50	$187.50
Purchase #2	$136.54	12.322%	$153.3645	$153.36	$153.35	$153.40
Purchase #3	$105.70	3.307%	$109.1955	$109.20	$109.20	$109.20
Purchase #4	$145.82	10.167%	$160.6455	$160.65	$160.65	$160.60
Purchase #5	$90.93	13.293%	$103.0173	$103.02	$103.00	$103.00
Purchase #6	$177.44	7.867%	$191.3992	$191.40	$191.40	$191.40
Purchase #7	$197.33	3.527%	$204.2898	$204.29	$204.30	$204.30
7 purchase totals =	$1,033.11		$1,109.4133	$1,109.42	$1,109.40	$1,109.40