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	$41.67	5.362%	$43.9043	$43.90	$43.90	$43.90
Purchase #2	$26.61	9.191%	$29.0557	$29.06	$29.05	$29.10
Purchase #3	$21.69	7.333%	$23.2805	$23.28	$23.30	$23.30
Purchase #4	$63.43	13.265%	$71.844	$71.84	$71.85	$71.80
Purchase #5	$80.25	5.698%	$84.8226	$84.82	$84.80	$84.80
Purchase #6	$131.59	5.798%	$139.2196	$139.22	$139.20	$139.20
Purchase #7	$90.50	11.534%	$100.9383	$100.94	$100.95	$100.90
7 purchase totals =	$455.74		$493.0650	$493.06	$493.05	$493.00