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	$235.79	9.652%	$258.5485	$258.55	$258.55	$258.50
Purchase #2	$187.36	4.715%	$196.194	$196.19	$196.20	$196.20
Purchase #3	$148.76	6.354%	$158.2122	$158.21	$158.20	$158.20
Purchase #4	$239.53	10.457%	$264.5777	$264.58	$264.60	$264.60
Purchase #5	$52.53	8.208%	$56.8417	$56.84	$56.85	$56.80
Purchase #6	$70.63	11.388%	$78.6733	$78.67	$78.65	$78.70
Purchase #7	$144.50	5.625%	$152.6281	$152.63	$152.65	$152.60
7 purchase totals =	$1,079.10		$1,165.6755	$1,165.67	$1,165.70	$1,165.60