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	$111.89	5.686%	$118.2521	$118.25	$118.25	$118.30
Purchase #2	$217.88	12.832%	$245.8384	$245.84	$245.85	$245.80
Purchase #3	$126.75	8.452%	$137.4629	$137.46	$137.45	$137.50
Purchase #4	$249.34	10.527%	$275.588	$275.59	$275.60	$275.60
Purchase #5	$49.59	11.716%	$55.4	$55.40	$55.40	$55.40
Purchase #6	$208.67	9.188%	$227.8426	$227.84	$227.85	$227.80
Purchase #7	$76.59	13.459%	$86.8982	$86.90	$86.90	$86.90
7 purchase totals =	$1,040.71		$1,147.2822	$1,147.28	$1,147.30	$1,147.30