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	$156.59	13.309%	$177.4306	$177.43	$177.45	$177.40
Purchase #2	$155.84	10.781%	$172.6411	$172.64	$172.65	$172.60
Purchase #3	$79.78	4.665%	$83.5017	$83.50	$83.50	$83.50
Purchase #4	$93.25	13.102%	$105.4676	$105.47	$105.45	$105.50
Purchase #5	$201.45	6.754%	$215.0559	$215.06	$215.05	$215.10
Purchase #6	$109.30	10.214%	$120.4639	$120.46	$120.45	$120.50
Purchase #7	$44.35	9.297%	$48.4732	$48.47	$48.45	$48.50
7 purchase totals =	$840.56		$923.0340	$923.03	$923.00	$923.10