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	$158.25	7.188%	$169.625	$169.63	$169.65	$169.60
Purchase #2	$116.40	13.339%	$131.9266	$131.93	$131.95	$131.90
Purchase #3	$82.53	9.602%	$90.4545	$90.45	$90.45	$90.50
Purchase #4	$215.78	10.485%	$238.4045	$238.40	$238.40	$238.40
Purchase #5	$66.94	7.299%	$71.826	$71.83	$71.85	$71.80
Purchase #6	$97.96	6.608%	$104.4332	$104.43	$104.45	$104.40
Purchase #7	$61.55	3.112%	$63.4654	$63.47	$63.45	$63.50
7 purchase totals =	$799.41		$870.1352	$870.14	$870.20	$870.10