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	$221.34	12.750%	$249.5609	$249.56	$249.55	$249.60
Purchase #2	$96.80	13.215%	$109.5921	$109.59	$109.60	$109.60
Purchase #3	$184.26	3.264%	$190.2742	$190.27	$190.25	$190.30
Purchase #4	$18.33	9.564%	$20.0831	$20.08	$20.10	$20.10
Purchase #5	$169.89	6.555%	$181.0263	$181.03	$181.05	$181.00
Purchase #6	$69.99	12.472%	$78.7192	$78.72	$78.70	$78.70
Purchase #7	$100.50	8.659%	$109.2023	$109.20	$109.20	$109.20
7 purchase totals =	$861.11		$938.4581	$938.45	$938.45	$938.50