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	$104.85	12.468%	$117.9227	$117.92	$117.90	$117.90
Purchase #2	$57.59	8.682%	$62.59	$62.59	$62.60	$62.60
Purchase #3	$61.62	3.262%	$63.63	$63.63	$63.65	$63.60
Purchase #4	$39.98	7.275%	$42.8885	$42.89	$42.90	$42.90
Purchase #5	$21.42	9.714%	$23.5007	$23.50	$23.50	$23.50
Purchase #6	$184.32	3.624%	$190.9998	$191.00	$191.00	$191.00
Purchase #7	$138.45	9.321%	$151.3549	$151.35	$151.35	$151.40
7 purchase totals =	$608.23		$652.8866	$652.88	$652.90	$652.90