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	$152.31	10.662%	$168.5493	$168.55	$168.55	$168.50
Purchase #2	$33.49	12.474%	$37.6675	$37.67	$37.65	$37.70
Purchase #3	$92.85	12.278%	$104.2501	$104.25	$104.25	$104.30
Purchase #4	$154.42	11.766%	$172.5891	$172.59	$172.60	$172.60
Purchase #5	$33.76	3.350%	$34.891	$34.89	$34.90	$34.90
Purchase #6	$140.59	5.630%	$148.5052	$148.51	$148.50	$148.50
Purchase #7	$147.85	10.716%	$163.6936	$163.69	$163.70	$163.70
7 purchase totals =	$755.27		$830.1458	$830.15	$830.15	$830.20