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	$38.77	8.521%	$42.0736	$42.07	$42.05	$42.10
Purchase #2	$113.29	12.350%	$127.2813	$127.28	$127.30	$127.30
Purchase #3	$12.28	9.749%	$13.4772	$13.48	$13.50	$13.50
Purchase #4	$238.67	11.856%	$266.9667	$266.97	$266.95	$267.00
Purchase #5	$129.48	8.477%	$140.456	$140.46	$140.45	$140.50
Purchase #6	$216.55	5.669%	$228.8262	$228.83	$228.85	$228.80
Purchase #7	$232.31	12.705%	$261.825	$261.83	$261.85	$261.80
7 purchase totals =	$981.35		$1,080.9060	$1,080.92	$1,080.95	$1,081.00