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	$244.51	9.588%	$267.9536	$267.95	$267.95	$268.00
Purchase #2	$174.49	13.736%	$198.4579	$198.46	$198.45	$198.50
Purchase #3	$44.68	6.461%	$47.5668	$47.57	$47.55	$47.60
Purchase #4	$188.85	11.382%	$210.3449	$210.34	$210.35	$210.30
Purchase #5	$206.48	10.151%	$227.4398	$227.44	$227.45	$227.40
Purchase #6	$65.32	11.630%	$72.9167	$72.92	$72.90	$72.90
Purchase #7	$50.59	9.217%	$55.2529	$55.25	$55.25	$55.30
7 purchase totals =	$974.92		$1,079.9326	$1,079.93	$1,079.90	$1,080.00