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	$57.98	4.204%	$60.4175	$60.42	$60.40	$60.40
Purchase #2	$86.44	4.676%	$90.4819	$90.48	$90.50	$90.50
Purchase #3	$18.78	12.869%	$21.1968	$21.20	$21.20	$21.20
Purchase #4	$108.30	9.762%	$118.8722	$118.87	$118.85	$118.90
Purchase #5	$68.30	5.830%	$72.2819	$72.28	$72.30	$72.30
Purchase #6	$226.94	6.868%	$242.5262	$242.53	$242.55	$242.50
Purchase #7	$228.60	12.662%	$257.5453	$257.55	$257.55	$257.50
7 purchase totals =	$795.34		$863.3218	$863.33	$863.35	$863.30