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	$132.29	7.178%	$141.7858	$141.79	$141.80	$141.80
Purchase #2	$227.97	13.473%	$258.6844	$258.68	$258.70	$258.70
Purchase #3	$105.40	4.293%	$109.9248	$109.92	$109.90	$109.90
Purchase #4	$135.31	5.828%	$143.1959	$143.20	$143.20	$143.20
Purchase #5	$234.58	9.397%	$256.6235	$256.62	$256.60	$256.60
Purchase #6	$63.77	11.346%	$71.0053	$71.01	$71.00	$71.00
Purchase #7	$105.65	3.259%	$109.0931	$109.09	$109.10	$109.10
7 purchase totals =	$1,004.97		$1,090.3128	$1,090.31	$1,090.30	$1,090.30