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	$104.54	13.356%	$118.5024	$118.50	$118.50	$118.50
Purchase #2	$31.57	4.802%	$33.086	$33.09	$33.10	$33.10
Purchase #3	$115.90	10.249%	$127.7786	$127.78	$127.80	$127.80
Purchase #4	$33.31	12.733%	$37.5514	$37.55	$37.55	$37.60
Purchase #5	$183.51	7.826%	$197.8715	$197.87	$197.85	$197.90
Purchase #6	$99.67	10.204%	$109.8403	$109.84	$109.85	$109.80
Purchase #7	$228.85	9.827%	$251.3391	$251.34	$251.35	$251.30
7 purchase totals =	$797.35		$875.9693	$875.97	$876.00	$876.00