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	$79.58	13.128%	$90.0273	$90.03	$90.05	$90.00
Purchase #2	$19.75	6.835%	$21.0999	$21.10	$21.10	$21.10
Purchase #3	$143.54	8.127%	$155.2055	$155.21	$155.20	$155.20
Purchase #4	$79.77	3.382%	$82.4678	$82.47	$82.45	$82.50
Purchase #5	$155.25	6.289%	$165.0137	$165.01	$165.00	$165.00
Purchase #6	$233.46	3.690%	$242.0747	$242.07	$242.05	$242.10
Purchase #7	$77.83	13.402%	$88.2608	$88.26	$88.25	$88.30
7 purchase totals =	$789.18		$844.1497	$844.15	$844.10	$844.20