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	$95.97	3.196%	$99.0372	$99.04	$99.05	$99.00
Purchase #2	$85.86	4.277%	$89.5322	$89.53	$89.55	$89.50
Purchase #3	$47.80	6.667%	$50.9868	$50.99	$51.00	$51.00
Purchase #4	$224.31	9.192%	$244.9286	$244.93	$244.95	$244.90
Purchase #5	$110.65	4.393%	$115.5109	$115.51	$115.50	$115.50
Purchase #6	$139.84	13.379%	$158.5492	$158.55	$158.55	$158.50
Purchase #7	$19.76	10.436%	$21.8222	$21.82	$21.80	$21.80
7 purchase totals =	$724.19		$780.3671	$780.37	$780.40	$780.20