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	$115.47	13.458%	$131.01	$131.01	$131.00	$131.00
Purchase #2	$97.99	13.792%	$111.5048	$111.50	$111.50	$111.50
Purchase #3	$166.82	12.694%	$187.9961	$188.00	$188.00	$188.00
Purchase #4	$206.71	7.527%	$222.2691	$222.27	$222.25	$222.30
Purchase #5	$7.52	12.182%	$8.4361	$8.44	$8.45	$8.40
Purchase #6	$61.97	4.334%	$64.6558	$64.66	$64.65	$64.70
Purchase #7	$86.43	7.174%	$92.6305	$92.63	$92.65	$92.60
7 purchase totals =	$742.91		$818.5024	$818.51	$818.50	$818.50