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	$176.89	3.382%	$182.8724	$182.87	$182.85	$182.90
Purchase #2	$249.69	13.474%	$283.3332	$283.33	$283.35	$283.30
Purchase #3	$205.64	11.657%	$229.6115	$229.61	$229.60	$229.60
Purchase #4	$126.98	10.391%	$140.1745	$140.17	$140.15	$140.20
Purchase #5	$41.50	5.235%	$43.6725	$43.67	$43.65	$43.70
Purchase #6	$221.78	9.767%	$243.4413	$243.44	$243.45	$243.40
Purchase #7	$19.42	8.557%	$21.0818	$21.08	$21.10	$21.10
7 purchase totals =	$1,041.90		$1,144.1872	$1,144.17	$1,144.15	$1,144.20