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	$38.65	4.668%	$40.4542	$40.45	$40.45	$40.50
Purchase #2	$173.47	7.736%	$186.8896	$186.89	$186.90	$186.90
Purchase #3	$98.61	6.769%	$105.2849	$105.28	$105.30	$105.30
Purchase #4	$19.57	12.169%	$21.9515	$21.95	$21.95	$22.00
Purchase #5	$112.85	7.580%	$121.404	$121.40	$121.40	$121.40
Purchase #6	$122.93	9.394%	$134.478	$134.48	$134.50	$134.50
Purchase #7	$54.29	5.345%	$57.1918	$57.19	$57.20	$57.20
7 purchase totals =	$620.37		$667.6540	$667.64	$667.70	$667.80