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	$58.61	13.486%	$66.5141	$66.51	$66.50	$66.50
Purchase #2	$97.99	7.552%	$105.3902	$105.39	$105.40	$105.40
Purchase #3	$19.96	11.383%	$22.232	$22.23	$22.25	$22.20
Purchase #4	$59.69	5.630%	$63.0505	$63.05	$63.05	$63.10
Purchase #5	$138.37	3.626%	$143.3873	$143.39	$143.40	$143.40
Purchase #6	$81.51	9.690%	$89.4083	$89.41	$89.40	$89.40
Purchase #7	$5.32	8.567%	$5.7758	$5.78	$5.80	$5.80
7 purchase totals =	$461.45		$495.7582	$495.76	$495.80	$495.80