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	$65.45	11.257%	$72.8177	$72.82	$72.80	$72.80
Purchase #2	$189.39	11.838%	$211.81	$211.81	$211.80	$211.80
Purchase #3	$89.47	6.137%	$94.9608	$94.96	$94.95	$95.00
Purchase #4	$81.89	10.409%	$90.4139	$90.41	$90.40	$90.40
Purchase #5	$86.50	6.730%	$92.3215	$92.32	$92.30	$92.30
Purchase #6	$137.95	7.564%	$148.3845	$148.38	$148.40	$148.40
Purchase #7	$202.39	10.765%	$224.1773	$224.18	$224.20	$224.20
7 purchase totals =	$853.04		$934.8857	$934.88	$934.85	$934.90