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	$11.44	13.739%	$13.0117	$13.01	$13.00	$13.00
Purchase #2	$185.47	10.541%	$205.0204	$205.02	$205.00	$205.00
Purchase #3	$245.63	3.498%	$254.2221	$254.22	$254.20	$254.20
Purchase #4	$185.27	7.442%	$199.0578	$199.06	$199.05	$199.10
Purchase #5	$105.68	5.333%	$111.3159	$111.32	$111.30	$111.30
Purchase #6	$98.28	13.549%	$111.596	$111.60	$111.60	$111.60
Purchase #7	$146.52	5.208%	$154.1508	$154.15	$154.15	$154.20
7 purchase totals =	$978.29		$1,048.3747	$1,048.38	$1,048.30	$1,048.40