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	$137.37	9.467%	$150.3748	$150.37	$150.35	$150.40
Purchase #2	$83.96	9.387%	$91.8413	$91.84	$91.85	$91.80
Purchase #3	$38.45	5.589%	$40.599	$40.60	$40.60	$40.60
Purchase #4	$197.44	10.363%	$217.9007	$217.90	$217.90	$217.90
Purchase #5	$36.68	3.353%	$37.9099	$37.91	$37.90	$37.90
Purchase #6	$47.32	5.792%	$50.0608	$50.06	$50.05	$50.10
Purchase #7	$232.65	11.237%	$258.7929	$258.79	$258.80	$258.80
7 purchase totals =	$773.87		$847.4794	$847.47	$847.45	$847.50