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	$81.47	9.481%	$89.1942	$89.19	$89.20	$89.20
Purchase #2	$130.72	7.565%	$140.609	$140.61	$140.60	$140.60
Purchase #3	$124.32	10.168%	$136.9609	$136.96	$136.95	$137.00
Purchase #4	$50.92	10.460%	$56.2462	$56.25	$56.25	$56.20
Purchase #5	$77.92	9.604%	$85.4034	$85.40	$85.40	$85.40
Purchase #6	$207.60	12.265%	$233.0621	$233.06	$233.05	$233.10
Purchase #7	$130.50	9.874%	$143.3856	$143.39	$143.40	$143.40
7 purchase totals =	$803.45		$884.8614	$884.86	$884.85	$884.90