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	$29.56	6.866%	$31.5896	$31.59	$31.60	$31.60
Purchase #2	$89.51	12.113%	$100.3523	$100.35	$100.35	$100.40
Purchase #3	$66.59	9.576%	$72.9667	$72.97	$72.95	$73.00
Purchase #4	$70.38	9.367%	$76.9725	$76.97	$76.95	$77.00
Purchase #5	$104.63	9.436%	$114.5029	$114.50	$114.50	$114.50
Purchase #6	$55.52	11.186%	$61.7305	$61.73	$61.75	$61.70
Purchase #7	$180.55	3.604%	$187.057	$187.06	$187.05	$187.10
7 purchase totals =	$596.74		$645.1715	$645.17	$645.15	$645.30