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	$160.72	5.209%	$169.0919	$169.09	$169.10	$169.10
Purchase #2	$56.82	12.221%	$63.764	$63.76	$63.75	$63.80
Purchase #3	$162.96	5.359%	$171.693	$171.69	$171.70	$171.70
Purchase #4	$20.69	10.180%	$22.7962	$22.80	$22.80	$22.80
Purchase #5	$102.29	3.346%	$105.7126	$105.71	$105.70	$105.70
Purchase #6	$119.48	3.641%	$123.8303	$123.83	$123.85	$123.80
Purchase #7	$119.54	10.514%	$132.1084	$132.11	$132.10	$132.10
7 purchase totals =	$742.50		$788.9964	$788.99	$789.00	$789.00