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	$212.82	12.281%	$238.9564	$238.96	$238.95	$239.00
Purchase #2	$52.27	12.498%	$58.8027	$58.80	$58.80	$58.80
Purchase #3	$212.79	7.821%	$229.4323	$229.43	$229.45	$229.40
Purchase #4	$144.45	12.109%	$161.9415	$161.94	$161.95	$161.90
Purchase #5	$140.25	9.704%	$153.8599	$153.86	$153.85	$153.90
Purchase #6	$94.75	6.172%	$100.598	$100.60	$100.60	$100.60
Purchase #7	$159.57	8.165%	$172.5989	$172.60	$172.60	$172.60
7 purchase totals =	$1,016.90		$1,116.1897	$1,116.19	$1,116.20	$1,116.20