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	$245.37	5.175%	$258.0679	$258.07	$258.05	$258.10
Purchase #2	$130.78	8.853%	$142.358	$142.36	$142.35	$142.40
Purchase #3	$44.73	6.453%	$47.6164	$47.62	$47.60	$47.60
Purchase #4	$154.67	11.699%	$172.7648	$172.76	$172.75	$172.80
Purchase #5	$162.76	5.445%	$171.6223	$171.62	$171.60	$171.60
Purchase #6	$99.91	3.429%	$103.3359	$103.34	$103.35	$103.30
Purchase #7	$230.58	12.830%	$260.1634	$260.16	$260.15	$260.20
7 purchase totals =	$1,068.80		$1,155.9287	$1,155.93	$1,155.85	$1,156.00