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	$93.97	6.754%	$100.3167	$100.32	$100.30	$100.30
Purchase #2	$172.55	10.808%	$191.1992	$191.20	$191.20	$191.20
Purchase #3	$170.68	10.185%	$188.0638	$188.06	$188.05	$188.10
Purchase #4	$53.83	5.400%	$56.7368	$56.74	$56.75	$56.70
Purchase #5	$80.93	6.829%	$86.4567	$86.46	$86.45	$86.50
Purchase #6	$176.92	11.627%	$197.4905	$197.49	$197.50	$197.50
Purchase #7	$37.69	7.518%	$40.5235	$40.52	$40.50	$40.50
7 purchase totals =	$786.57		$860.7872	$860.79	$860.75	$860.80