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	$144.33	10.620%	$159.6578	$159.66	$159.65	$159.70
Purchase #2	$37.89	9.856%	$41.6244	$41.62	$41.60	$41.60
Purchase #3	$51.79	8.380%	$56.13	$56.13	$56.15	$56.10
Purchase #4	$220.70	8.702%	$239.9053	$239.91	$239.90	$239.90
Purchase #5	$111.27	11.670%	$124.2552	$124.26	$124.25	$124.30
Purchase #6	$107.55	5.563%	$113.533	$113.53	$113.55	$113.50
Purchase #7	$78.68	8.663%	$85.496	$85.50	$85.50	$85.50
7 purchase totals =	$752.21		$820.6017	$820.61	$820.60	$820.60