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	$18.86	9.431%	$20.6387	$20.64	$20.65	$20.60
Purchase #2	$163.85	13.459%	$185.9026	$185.90	$185.90	$185.90
Purchase #3	$90.61	11.193%	$100.752	$100.75	$100.75	$100.80
Purchase #4	$161.89	10.376%	$178.6877	$178.69	$178.70	$178.70
Purchase #5	$219.67	13.528%	$249.387	$249.39	$249.40	$249.40
Purchase #6	$215.38	7.374%	$231.2621	$231.26	$231.25	$231.30
Purchase #7	$158.68	8.658%	$172.4185	$172.42	$172.40	$172.40
7 purchase totals =	$1,028.94		$1,139.0486	$1,139.05	$1,139.05	$1,139.10