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	$54.65	9.624%	$59.9095	$59.91	$59.90	$59.90
Purchase #2	$182.26	6.561%	$194.2181	$194.22	$194.20	$194.20
Purchase #3	$34.84	12.780%	$39.2926	$39.29	$39.30	$39.30
Purchase #4	$30.87	3.750%	$32.0276	$32.03	$32.05	$32.00
Purchase #5	$36.93	10.793%	$40.9159	$40.92	$40.90	$40.90
Purchase #6	$82.55	4.196%	$86.0138	$86.01	$86.00	$86.00
Purchase #7	$170.34	3.667%	$176.5864	$176.59	$176.60	$176.60
7 purchase totals =	$592.44		$628.9639	$628.97	$628.95	$628.90