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	$97.50	12.641%	$109.825	$109.83	$109.85	$109.80
Purchase #2	$78.79	13.634%	$89.5322	$89.53	$89.55	$89.50
Purchase #3	$249.47	12.789%	$281.3747	$281.37	$281.35	$281.40
Purchase #4	$176.32	7.437%	$189.4329	$189.43	$189.45	$189.40
Purchase #5	$63.86	7.705%	$68.7804	$68.78	$68.80	$68.80
Purchase #6	$83.48	6.667%	$89.0456	$89.05	$89.05	$89.00
Purchase #7	$156.48	7.410%	$168.0752	$168.08	$168.10	$168.10
7 purchase totals =	$905.90		$996.0660	$996.07	$996.15	$996.00