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	$5.87	3.722%	$6.0885	$6.09	$6.10	$6.10
Purchase #2	$54.52	4.312%	$56.8709	$56.87	$56.85	$56.90
Purchase #3	$227.64	6.703%	$242.8987	$242.90	$242.90	$242.90
Purchase #4	$198.54	10.470%	$219.3271	$219.33	$219.35	$219.30
Purchase #5	$239.70	6.750%	$255.8798	$255.88	$255.90	$255.90
Purchase #6	$111.31	5.861%	$117.8339	$117.83	$117.85	$117.80
Purchase #7	$217.97	12.184%	$244.5275	$244.53	$244.55	$244.50
7 purchase totals =	$1,055.55		$1,143.4264	$1,143.43	$1,143.50	$1,143.40