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	$207.46	13.220%	$234.8862	$234.89	$234.90	$234.90
Purchase #2	$47.31	7.418%	$50.8195	$50.82	$50.80	$50.80
Purchase #3	$31.53	10.356%	$34.7952	$34.80	$34.80	$34.80
Purchase #4	$32.59	12.312%	$36.6025	$36.60	$36.60	$36.60
Purchase #5	$34.69	9.152%	$37.8648	$37.86	$37.85	$37.90
Purchase #6	$71.50	9.212%	$78.0866	$78.09	$78.10	$78.10
Purchase #7	$94.81	12.791%	$106.9371	$106.94	$106.95	$106.90
7 purchase totals =	$519.89		$579.9919	$580.00	$580.00	$580.00