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	$146.71	6.592%	$156.3811	$156.38	$156.40	$156.40
Purchase #2	$172.48	4.558%	$180.3416	$180.34	$180.35	$180.30
Purchase #3	$172.79	9.228%	$188.7351	$188.74	$188.75	$188.70
Purchase #4	$13.43	3.800%	$13.9403	$13.94	$13.95	$13.90
Purchase #5	$250.91	6.208%	$266.4865	$266.49	$266.50	$266.50
Purchase #6	$137.46	11.666%	$153.4961	$153.50	$153.50	$153.50
Purchase #7	$9.59	12.817%	$10.8192	$10.82	$10.80	$10.80
7 purchase totals =	$903.37		$970.1999	$970.21	$970.25	$970.10