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	$182.61	13.207%	$206.7273	$206.73	$206.75	$206.70
Purchase #2	$74.68	5.208%	$78.5693	$78.57	$78.55	$78.60
Purchase #3	$96.64	13.314%	$109.5066	$109.51	$109.50	$109.50
Purchase #4	$230.28	9.712%	$252.6448	$252.64	$252.65	$252.60
Purchase #5	$147.68	7.503%	$158.7604	$158.76	$158.75	$158.80
Purchase #6	$176.82	11.329%	$196.8519	$196.85	$196.85	$196.90
Purchase #7	$212.61	11.404%	$236.856	$236.86	$236.85	$236.90
7 purchase totals =	$1,121.32		$1,239.9163	$1,239.92	$1,239.90	$1,240.00