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	$127.43	8.186%	$137.8614	$137.86	$137.85	$137.90
Purchase #2	$225.77	12.124%	$253.1424	$253.14	$253.15	$253.10
Purchase #3	$112.45	9.399%	$123.0192	$123.02	$123.00	$123.00
Purchase #4	$30.64	10.180%	$33.7592	$33.76	$33.75	$33.80
Purchase #5	$82.85	12.484%	$93.193	$93.19	$93.20	$93.20
Purchase #6	$116.94	12.776%	$131.8803	$131.88	$131.90	$131.90
Purchase #7	$135.55	6.397%	$144.2211	$144.22	$144.20	$144.20
7 purchase totals =	$831.63		$917.0766	$917.07	$917.05	$917.10