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	$90.82	9.310%	$99.2753	$99.28	$99.30	$99.30
Purchase #2	$190.74	3.198%	$196.8399	$196.84	$196.85	$196.80
Purchase #3	$23.33	11.533%	$26.0206	$26.02	$26.00	$26.00
Purchase #4	$31.80	8.769%	$34.5885	$34.59	$34.60	$34.60
Purchase #5	$73.35	12.506%	$82.5232	$82.52	$82.50	$82.50
Purchase #6	$115.31	4.259%	$120.2211	$120.22	$120.20	$120.20
Purchase #7	$165.47	7.846%	$178.4528	$178.45	$178.45	$178.50
7 purchase totals =	$690.82		$737.9214	$737.92	$737.90	$737.90