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	$96.45	12.308%	$108.3211	$108.32	$108.30	$108.30
Purchase #2	$226.92	13.457%	$257.4566	$257.46	$257.45	$257.50
Purchase #3	$34.92	7.229%	$37.4444	$37.44	$37.45	$37.40
Purchase #4	$102.50	6.432%	$109.0928	$109.09	$109.10	$109.10
Purchase #5	$201.63	5.246%	$212.2075	$212.21	$212.20	$212.20
Purchase #6	$40.27	12.709%	$45.3879	$45.39	$45.40	$45.40
Purchase #7	$38.69	10.583%	$42.7846	$42.78	$42.80	$42.80
7 purchase totals =	$741.38		$812.6949	$812.69	$812.70	$812.70