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	$12.86	5.385%	$13.5525	$13.55	$13.55	$13.60
Purchase #2	$39.61	13.845%	$45.094	$45.09	$45.10	$45.10
Purchase #3	$228.56	13.633%	$259.7196	$259.72	$259.70	$259.70
Purchase #4	$245.28	9.118%	$267.6446	$267.64	$267.65	$267.60
Purchase #5	$132.84	9.397%	$145.323	$145.32	$145.30	$145.30
Purchase #6	$78.41	6.172%	$83.2495	$83.25	$83.25	$83.20
Purchase #7	$131.98	7.361%	$141.695	$141.70	$141.70	$141.70
7 purchase totals =	$869.54		$956.2782	$956.27	$956.25	$956.20