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	$122.77	12.822%	$138.5116	$138.51	$138.50	$138.50
Purchase #2	$44.34	13.519%	$50.3343	$50.33	$50.35	$50.30
Purchase #3	$20.92	3.381%	$21.6273	$21.63	$21.65	$21.60
Purchase #4	$52.62	13.398%	$59.67	$59.67	$59.65	$59.70
Purchase #5	$117.59	8.371%	$127.4335	$127.43	$127.45	$127.40
Purchase #6	$107.71	7.745%	$116.0521	$116.05	$116.05	$116.10
Purchase #7	$36.48	9.154%	$39.8194	$39.82	$39.80	$39.80
7 purchase totals =	$502.43		$553.4482	$553.44	$553.45	$553.40