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	$187.31	10.324%	$206.6479	$206.65	$206.65	$206.60
Purchase #2	$90.42	4.212%	$94.2285	$94.23	$94.25	$94.20
Purchase #3	$250.92	13.605%	$285.0577	$285.06	$285.05	$285.10
Purchase #4	$153.49	9.809%	$168.5458	$168.55	$168.55	$168.50
Purchase #5	$78.43	5.773%	$82.9578	$82.96	$82.95	$83.00
Purchase #6	$129.50	12.757%	$146.0203	$146.02	$146.00	$146.00
Purchase #7	$112.78	9.406%	$123.3881	$123.39	$123.40	$123.40
7 purchase totals =	$1,002.85		$1,106.8461	$1,106.86	$1,106.85	$1,106.80