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	$136.59	11.384%	$152.1394	$152.14	$152.15	$152.10
Purchase #2	$108.82	3.537%	$112.669	$112.67	$112.65	$112.70
Purchase #3	$24.55	13.446%	$27.851	$27.85	$27.85	$27.90
Purchase #4	$56.33	9.348%	$61.5957	$61.60	$61.60	$61.60
Purchase #5	$240.93	12.412%	$270.8342	$270.83	$270.85	$270.80
Purchase #6	$139.94	13.514%	$158.8515	$158.85	$158.85	$158.90
Purchase #7	$131.78	5.231%	$138.6734	$138.67	$138.65	$138.70
7 purchase totals =	$838.94		$922.6142	$922.61	$922.60	$922.70