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	$155.58	10.214%	$171.4709	$171.47	$171.45	$171.50
Purchase #2	$154.50	8.133%	$167.0655	$167.07	$167.05	$167.10
Purchase #3	$167.29	12.667%	$188.4806	$188.48	$188.50	$188.50
Purchase #4	$137.92	10.690%	$152.6636	$152.66	$152.65	$152.70
Purchase #5	$154.80	9.738%	$169.8744	$169.87	$169.85	$169.90
Purchase #6	$43.87	13.126%	$49.6284	$49.63	$49.65	$49.60
Purchase #7	$187.43	6.661%	$199.9147	$199.91	$199.90	$199.90
7 purchase totals =	$1,001.39		$1,099.0981	$1,099.09	$1,099.05	$1,099.20