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	$113.49	3.870%	$117.8821	$117.88	$117.90	$117.90
Purchase #2	$29.77	9.177%	$32.502	$32.50	$32.50	$32.50
Purchase #3	$210.71	4.306%	$219.7832	$219.78	$219.80	$219.80
Purchase #4	$100.29	5.556%	$105.8621	$105.86	$105.85	$105.90
Purchase #5	$13.99	10.798%	$15.5006	$15.50	$15.50	$15.50
Purchase #6	$234.81	5.521%	$247.7739	$247.77	$247.75	$247.80
Purchase #7	$131.49	11.641%	$146.7968	$146.80	$146.80	$146.80
7 purchase totals =	$834.55		$886.1007	$886.09	$886.10	$886.20