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	$236.31	8.618%	$256.6752	$256.68	$256.70	$256.70
Purchase #2	$128.72	12.421%	$144.7083	$144.71	$144.70	$144.70
Purchase #3	$95.49	8.102%	$103.2266	$103.23	$103.25	$103.20
Purchase #4	$61.31	9.783%	$67.308	$67.31	$67.30	$67.30
Purchase #5	$74.45	5.620%	$78.6341	$78.63	$78.65	$78.60
Purchase #6	$99.88	9.582%	$109.4505	$109.45	$109.45	$109.50
Purchase #7	$87.35	5.652%	$92.287	$92.29	$92.30	$92.30
7 purchase totals =	$783.51		$852.2897	$852.30	$852.35	$852.30