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	$35.35	13.531%	$40.1332	$40.13	$40.15	$40.10
Purchase #2	$187.30	12.455%	$210.6282	$210.63	$210.65	$210.60
Purchase #3	$147.29	4.758%	$154.2981	$154.30	$154.30	$154.30
Purchase #4	$226.55	4.379%	$236.4706	$236.47	$236.45	$236.50
Purchase #5	$35.89	5.444%	$37.8439	$37.84	$37.85	$37.80
Purchase #6	$122.34	12.496%	$137.6276	$137.63	$137.65	$137.60
Purchase #7	$171.42	7.682%	$184.5885	$184.59	$184.60	$184.60
7 purchase totals =	$926.14		$1,001.5901	$1,001.59	$1,001.65	$1,001.50