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	$48.54	12.288%	$54.5046	$54.50	$54.50	$54.50
Purchase #2	$144.77	11.384%	$161.2506	$161.25	$161.25	$161.30
Purchase #3	$137.69	10.580%	$152.2576	$152.26	$152.25	$152.30
Purchase #4	$195.88	6.373%	$208.3634	$208.36	$208.35	$208.40
Purchase #5	$40.65	3.667%	$42.1406	$42.14	$42.15	$42.10
Purchase #6	$213.49	6.726%	$227.8493	$227.85	$227.85	$227.80
Purchase #7	$159.90	4.203%	$166.6206	$166.62	$166.60	$166.60
7 purchase totals =	$940.92		$1,012.9867	$1,012.98	$1,012.95	$1,013.00