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	$111.78	5.286%	$117.6887	$117.69	$117.70	$117.70
Purchase #2	$208.44	5.225%	$219.331	$219.33	$219.35	$219.30
Purchase #3	$42.48	5.409%	$44.7777	$44.78	$44.80	$44.80
Purchase #4	$54.73	9.472%	$59.914	$59.91	$59.90	$59.90
Purchase #5	$18.86	13.709%	$21.4455	$21.45	$21.45	$21.40
Purchase #6	$69.69	12.777%	$78.5943	$78.59	$78.60	$78.60
Purchase #7	$229.57	3.106%	$236.7004	$236.70	$236.70	$236.70
7 purchase totals =	$735.55		$778.4516	$778.45	$778.50	$778.40