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	$90.98	10.400%	$100.4419	$100.44	$100.45	$100.40
Purchase #2	$153.92	7.398%	$165.307	$165.31	$165.30	$165.30
Purchase #3	$21.43	6.871%	$22.9025	$22.90	$22.90	$22.90
Purchase #4	$241.90	8.648%	$262.8195	$262.82	$262.80	$262.80
Purchase #5	$70.45	7.632%	$75.8267	$75.83	$75.85	$75.80
Purchase #6	$112.68	9.654%	$123.5581	$123.56	$123.55	$123.60
Purchase #7	$60.54	9.369%	$66.212	$66.21	$66.20	$66.20
7 purchase totals =	$751.90		$817.0677	$817.07	$817.05	$817.00