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	$38.72	4.622%	$40.5096	$40.51	$40.50	$40.50
Purchase #2	$244.77	5.387%	$257.9558	$257.96	$257.95	$258.00
Purchase #3	$55.33	4.602%	$57.8763	$57.88	$57.90	$57.90
Purchase #4	$162.77	11.225%	$181.0409	$181.04	$181.05	$181.00
Purchase #5	$64.71	4.827%	$67.8336	$67.83	$67.85	$67.80
Purchase #6	$89.53	5.688%	$94.6225	$94.62	$94.60	$94.60
Purchase #7	$205.65	9.451%	$225.086	$225.09	$225.10	$225.10
7 purchase totals =	$861.48		$924.9247	$924.93	$924.95	$924.90