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	$16.70	9.822%	$18.3403	$18.34	$18.35	$18.30
Purchase #2	$156.92	9.179%	$171.3237	$171.32	$171.30	$171.30
Purchase #3	$103.51	12.153%	$116.0896	$116.09	$116.10	$116.10
Purchase #4	$239.63	3.411%	$247.8038	$247.80	$247.80	$247.80
Purchase #5	$149.76	11.648%	$167.204	$167.20	$167.20	$167.20
Purchase #6	$155.39	6.795%	$165.9488	$165.95	$165.95	$165.90
Purchase #7	$100.90	10.280%	$111.2725	$111.27	$111.25	$111.30
7 purchase totals =	$922.81		$997.9827	$997.97	$997.95	$997.90