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	$102.59	3.802%	$106.4905	$106.49	$106.50	$106.50
Purchase #2	$17.40	9.436%	$19.0419	$19.04	$19.05	$19.00
Purchase #3	$152.67	6.449%	$162.5157	$162.52	$162.50	$162.50
Purchase #4	$205.93	10.290%	$227.1202	$227.12	$227.10	$227.10
Purchase #5	$155.38	8.359%	$168.3682	$168.37	$168.35	$168.40
Purchase #6	$39.64	6.126%	$42.0683	$42.07	$42.05	$42.10
Purchase #7	$103.37	8.187%	$111.8329	$111.83	$111.85	$111.80
7 purchase totals =	$776.98		$837.4377	$837.44	$837.40	$837.40