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	$150.91	11.564%	$168.3612	$168.36	$168.35	$168.40
Purchase #2	$112.76	13.184%	$127.6263	$127.63	$127.65	$127.60
Purchase #3	$219.80	9.836%	$241.4195	$241.42	$241.40	$241.40
Purchase #4	$76.78	3.356%	$79.3567	$79.36	$79.35	$79.40
Purchase #5	$59.85	11.254%	$66.5855	$66.59	$66.60	$66.60
Purchase #6	$172.55	7.654%	$185.757	$185.76	$185.75	$185.80
Purchase #7	$78.75	11.478%	$87.7889	$87.79	$87.80	$87.80
7 purchase totals =	$871.40		$956.8951	$956.91	$956.90	$957.00