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	$35.83	13.294%	$40.5932	$40.59	$40.60	$40.60
Purchase #2	$212.83	13.628%	$241.8345	$241.83	$241.85	$241.80
Purchase #3	$230.94	6.345%	$245.5931	$245.59	$245.60	$245.60
Purchase #4	$33.31	3.725%	$34.5508	$34.55	$34.55	$34.60
Purchase #5	$101.69	8.588%	$110.4231	$110.42	$110.40	$110.40
Purchase #6	$221.84	5.793%	$234.6912	$234.69	$234.70	$234.70
Purchase #7	$85.85	12.557%	$96.6302	$96.63	$96.65	$96.60
7 purchase totals =	$922.29		$1,004.3161	$1,004.30	$1,004.35	$1,004.30