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	$41.26	3.349%	$42.6418	$42.64	$42.65	$42.60
Purchase #2	$43.51	4.167%	$45.3231	$45.32	$45.30	$45.30
Purchase #3	$70.74	4.785%	$74.1249	$74.12	$74.10	$74.10
Purchase #4	$186.45	11.731%	$208.3224	$208.32	$208.30	$208.30
Purchase #5	$42.39	3.649%	$43.9368	$43.94	$43.95	$43.90
Purchase #6	$40.49	4.838%	$42.4489	$42.45	$42.45	$42.40
Purchase #7	$244.97	7.509%	$263.3648	$263.36	$263.35	$263.40
7 purchase totals =	$669.81		$720.1627	$720.15	$720.10	$720.00