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	$132.31	8.464%	$143.5087	$143.51	$143.50	$143.50
Purchase #2	$172.94	4.392%	$180.5355	$180.54	$180.55	$180.50
Purchase #3	$53.73	10.322%	$59.276	$59.28	$59.30	$59.30
Purchase #4	$72.70	3.312%	$75.1078	$75.11	$75.10	$75.10
Purchase #5	$51.47	3.221%	$53.1278	$53.13	$53.15	$53.10
Purchase #6	$70.98	12.726%	$80.0129	$80.01	$80.00	$80.00
Purchase #7	$210.82	6.388%	$224.2872	$224.29	$224.30	$224.30
7 purchase totals =	$764.95		$815.8559	$815.87	$815.90	$815.80