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	$67.50	4.161%	$70.3087	$70.31	$70.30	$70.30
Purchase #2	$120.38	11.499%	$134.2225	$134.22	$134.20	$134.20
Purchase #3	$38.56	9.610%	$42.2656	$42.27	$42.25	$42.30
Purchase #4	$150.85	11.380%	$168.0167	$168.02	$168.00	$168.00
Purchase #5	$101.39	10.523%	$112.0593	$112.06	$112.05	$112.10
Purchase #6	$42.88	9.439%	$46.9274	$46.93	$46.95	$46.90
Purchase #7	$226.71	6.609%	$241.6933	$241.69	$241.70	$241.70
7 purchase totals =	$748.27		$815.4935	$815.50	$815.45	$815.50