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	$81.96	9.136%	$89.4479	$89.45	$89.45	$89.40
Purchase #2	$48.96	7.130%	$52.4508	$52.45	$52.45	$52.50
Purchase #3	$246.78	9.382%	$269.9329	$269.93	$269.95	$269.90
Purchase #4	$233.62	13.395%	$264.9134	$264.91	$264.90	$264.90
Purchase #5	$247.82	3.673%	$256.9224	$256.92	$256.90	$256.90
Purchase #6	$81.83	9.702%	$89.7691	$89.77	$89.75	$89.80
Purchase #7	$209.27	11.649%	$233.6479	$233.65	$233.65	$233.60
7 purchase totals =	$1,150.24		$1,257.0844	$1,257.08	$1,257.05	$1,257.00