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	$140.71	10.867%	$156.001	$156.00	$156.00	$156.00
Purchase #2	$134.85	13.861%	$153.5416	$153.54	$153.55	$153.50
Purchase #3	$210.50	5.719%	$222.5385	$222.54	$222.55	$222.50
Purchase #4	$70.51	12.500%	$79.3238	$79.32	$79.30	$79.30
Purchase #5	$213.36	4.107%	$222.1227	$222.12	$222.10	$222.10
Purchase #6	$129.54	10.336%	$142.9293	$142.93	$142.95	$142.90
Purchase #7	$146.30	12.149%	$164.074	$164.07	$164.05	$164.10
7 purchase totals =	$1,045.77		$1,140.5309	$1,140.52	$1,140.50	$1,140.40