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	$155.61	4.650%	$162.8459	$162.85	$162.85	$162.80
Purchase #2	$51.45	11.148%	$57.1856	$57.19	$57.20	$57.20
Purchase #3	$250.58	11.572%	$279.5771	$279.58	$279.60	$279.60
Purchase #4	$128.75	6.120%	$136.6295	$136.63	$136.65	$136.60
Purchase #5	$94.78	12.482%	$106.6104	$106.61	$106.60	$106.60
Purchase #6	$182.47	4.452%	$190.5936	$190.59	$190.60	$190.60
Purchase #7	$60.68	7.863%	$65.4513	$65.45	$65.45	$65.50
7 purchase totals =	$924.32		$998.8934	$998.90	$998.95	$998.90