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	$40.35	4.767%	$42.2735	$42.27	$42.25	$42.30
Purchase #2	$249.86	10.254%	$275.4806	$275.48	$275.50	$275.50
Purchase #3	$11.92	12.611%	$13.4232	$13.42	$13.40	$13.40
Purchase #4	$161.29	3.233%	$166.5045	$166.50	$166.50	$166.50
Purchase #5	$213.43	11.572%	$238.1281	$238.13	$238.15	$238.10
Purchase #6	$176.35	9.252%	$192.6659	$192.67	$192.65	$192.70
Purchase #7	$198.76	7.304%	$213.2774	$213.28	$213.30	$213.30
7 purchase totals =	$1,051.96		$1,141.7532	$1,141.75	$1,141.75	$1,141.80