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	$133.95	9.829%	$147.1159	$147.12	$147.10	$147.10
Purchase #2	$38.64	6.672%	$41.2181	$41.22	$41.20	$41.20
Purchase #3	$132.49	4.841%	$138.9038	$138.90	$138.90	$138.90
Purchase #4	$85.61	6.671%	$91.321	$91.32	$91.30	$91.30
Purchase #5	$58.89	6.873%	$62.9375	$62.94	$62.95	$62.90
Purchase #6	$154.88	6.444%	$164.8605	$164.86	$164.85	$164.90
Purchase #7	$191.89	13.307%	$217.4248	$217.42	$217.40	$217.40
7 purchase totals =	$796.35		$863.7816	$863.78	$863.70	$863.70