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	$138.91	4.312%	$144.8998	$144.90	$144.90	$144.90
Purchase #2	$115.36	7.456%	$123.9612	$123.96	$123.95	$124.00
Purchase #3	$134.89	9.633%	$147.884	$147.88	$147.90	$147.90
Purchase #4	$82.38	12.420%	$92.6116	$92.61	$92.60	$92.60
Purchase #5	$234.53	6.579%	$249.9597	$249.96	$249.95	$250.00
Purchase #6	$59.42	4.152%	$61.8871	$61.89	$61.90	$61.90
Purchase #7	$126.25	6.841%	$134.8868	$134.89	$134.90	$134.90
7 purchase totals =	$891.74		$956.0902	$956.09	$956.10	$956.20