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	$85.31	9.455%	$93.3761	$93.38	$93.40	$93.40
Purchase #2	$141.44	6.531%	$150.6774	$150.68	$150.70	$150.70
Purchase #3	$131.85	12.674%	$148.5607	$148.56	$148.55	$148.60
Purchase #4	$67.42	6.572%	$71.8508	$71.85	$71.85	$71.90
Purchase #5	$149.54	3.248%	$154.3971	$154.40	$154.40	$154.40
Purchase #6	$134.40	6.716%	$143.4263	$143.43	$143.45	$143.40
Purchase #7	$142.55	5.776%	$150.7837	$150.78	$150.80	$150.80
7 purchase totals =	$852.51		$913.0721	$913.08	$913.15	$913.20