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	$101.79	9.553%	$111.514	$111.51	$111.50	$111.50
Purchase #2	$198.53	8.356%	$215.1192	$215.12	$215.10	$215.10
Purchase #3	$58.68	10.411%	$64.7892	$64.79	$64.80	$64.80
Purchase #4	$217.62	5.752%	$230.1375	$230.14	$230.15	$230.10
Purchase #5	$34.30	10.219%	$37.8051	$37.81	$37.80	$37.80
Purchase #6	$101.58	10.342%	$112.0854	$112.09	$112.10	$112.10
Purchase #7	$92.91	6.424%	$98.8785	$98.88	$98.90	$98.90
7 purchase totals =	$805.41		$870.3289	$870.34	$870.35	$870.30