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	$68.99	7.298%	$74.0249	$74.02	$74.00	$74.00
Purchase #2	$166.93	7.136%	$178.8421	$178.84	$178.85	$178.80
Purchase #3	$181.58	5.697%	$191.9246	$191.92	$191.90	$191.90
Purchase #4	$103.49	10.617%	$114.4775	$114.48	$114.50	$114.50
Purchase #5	$17.29	6.119%	$18.348	$18.35	$18.35	$18.30
Purchase #6	$80.83	12.354%	$90.8157	$90.82	$90.80	$90.80
Purchase #7	$172.40	9.103%	$188.0936	$188.09	$188.10	$188.10
7 purchase totals =	$791.51		$856.5264	$856.52	$856.50	$856.40