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	$139.66	9.791%	$153.3341	$153.33	$153.35	$153.30
Purchase #2	$52.96	13.182%	$59.9412	$59.94	$59.95	$59.90
Purchase #3	$109.34	7.170%	$117.1797	$117.18	$117.20	$117.20
Purchase #4	$36.33	5.349%	$38.2733	$38.27	$38.25	$38.30
Purchase #5	$201.33	4.531%	$210.4523	$210.45	$210.45	$210.50
Purchase #6	$26.90	9.376%	$29.4221	$29.42	$29.40	$29.40
Purchase #7	$96.75	4.313%	$100.9228	$100.92	$100.90	$100.90
7 purchase totals =	$663.27		$709.5255	$709.51	$709.50	$709.50