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	$110.88	11.453%	$123.5791	$123.58	$123.60	$123.60
Purchase #2	$122.87	6.695%	$131.0961	$131.10	$131.10	$131.10
Purchase #3	$156.97	3.526%	$162.5048	$162.50	$162.50	$162.50
Purchase #4	$100.97	3.813%	$104.82	$104.82	$104.80	$104.80
Purchase #5	$24.35	6.314%	$25.8875	$25.89	$25.90	$25.90
Purchase #6	$136.88	3.487%	$141.653	$141.65	$141.65	$141.70
Purchase #7	$127.28	11.789%	$142.285	$142.29	$142.30	$142.30
7 purchase totals =	$780.20		$831.8255	$831.83	$831.85	$831.90