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	$100.85	13.545%	$114.5101	$114.51	$114.50	$114.50
Purchase #2	$105.33	7.848%	$113.5963	$113.60	$113.60	$113.60
Purchase #3	$219.50	3.749%	$227.7291	$227.73	$227.75	$227.70
Purchase #4	$121.28	6.106%	$128.6854	$128.69	$128.70	$128.70
Purchase #5	$121.44	6.105%	$128.8539	$128.85	$128.85	$128.90
Purchase #6	$138.34	7.655%	$148.9299	$148.93	$148.95	$148.90
Purchase #7	$141.74	11.664%	$158.2726	$158.27	$158.25	$158.30
7 purchase totals =	$948.48		$1,020.5773	$1,020.58	$1,020.60	$1,020.60