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	$123.38	13.347%	$139.8475	$139.85	$139.85	$139.80
Purchase #2	$144.37	13.868%	$164.3912	$164.39	$164.40	$164.40
Purchase #3	$104.38	4.585%	$109.1658	$109.17	$109.15	$109.20
Purchase #4	$219.67	3.691%	$227.778	$227.78	$227.80	$227.80
Purchase #5	$51.60	9.454%	$56.4783	$56.48	$56.50	$56.50
Purchase #6	$24.49	13.778%	$27.8642	$27.86	$27.85	$27.90
Purchase #7	$122.87	9.153%	$134.1163	$134.12	$134.10	$134.10
7 purchase totals =	$790.76		$859.6413	$859.65	$859.65	$859.70