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	$26.64	6.695%	$28.4235	$28.42	$28.40	$28.40
Purchase #2	$212.71	4.178%	$221.597	$221.60	$221.60	$221.60
Purchase #3	$87.96	13.111%	$99.4924	$99.49	$99.50	$99.50
Purchase #4	$17.50	7.752%	$18.8566	$18.86	$18.85	$18.90
Purchase #5	$177.29	7.641%	$190.8367	$190.84	$190.85	$190.80
Purchase #6	$197.45	10.178%	$217.5465	$217.55	$217.55	$217.50
Purchase #7	$200.36	12.377%	$225.1586	$225.16	$225.15	$225.20
7 purchase totals =	$919.91		$1,001.9113	$1,001.92	$1,001.90	$1,001.90