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	$234.76	3.575%	$243.1527	$243.15	$243.15	$243.20
Purchase #2	$207.58	10.743%	$229.8803	$229.88	$229.90	$229.90
Purchase #3	$40.51	13.509%	$45.9825	$45.98	$46.00	$46.00
Purchase #4	$136.64	4.392%	$142.6412	$142.64	$142.65	$142.60
Purchase #5	$229.56	11.329%	$255.5669	$255.57	$255.55	$255.60
Purchase #6	$219.92	4.306%	$229.3898	$229.39	$229.40	$229.40
Purchase #7	$211.28	9.176%	$230.6671	$230.67	$230.65	$230.70
7 purchase totals =	$1,280.25		$1,377.2805	$1,377.28	$1,377.30	$1,377.40