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	$124.70	4.138%	$129.8601	$129.86	$129.85	$129.90
Purchase #2	$196.59	7.189%	$210.7229	$210.72	$210.70	$210.70
Purchase #3	$164.35	12.339%	$184.6291	$184.63	$184.65	$184.60
Purchase #4	$52.75	13.468%	$59.8544	$59.85	$59.85	$59.90
Purchase #5	$128.80	8.436%	$139.6656	$139.67	$139.65	$139.70
Purchase #6	$103.52	5.356%	$109.0645	$109.06	$109.05	$109.10
Purchase #7	$76.48	4.510%	$79.9292	$79.93	$79.95	$79.90
7 purchase totals =	$847.19		$913.7258	$913.72	$913.70	$913.80