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	$114.25	12.851%	$128.9323	$128.93	$128.95	$128.90
Purchase #2	$237.30	6.397%	$252.4801	$252.48	$252.50	$252.50
Purchase #3	$82.25	8.655%	$89.3687	$89.37	$89.35	$89.40
Purchase #4	$91.34	6.866%	$97.6114	$97.61	$97.60	$97.60
Purchase #5	$150.71	3.599%	$156.1341	$156.13	$156.15	$156.10
Purchase #6	$41.99	3.589%	$43.497	$43.50	$43.50	$43.50
Purchase #7	$49.72	4.721%	$52.0673	$52.07	$52.05	$52.10
7 purchase totals =	$767.56		$820.0909	$820.09	$820.10	$820.10